Hi,
To install the installer you need to:
Then you can disable the untrusted software again.
@jameson gave a good answer about presence of Storeman and its installer in the official store. In short, they are not allowed due to use of restricted APIs.
Awesome!
The setting is System → Security → Untrusted software.
I launched the phone’s web browser, typed in “https://openrepos.net” (typing anything on a touchscreen makes me barf in my mouth so I didn’t type the whole URL-Path to the Installer), located the search form (with the help of a desktop browser, lol), fumbled through to the package page, tapped the noarch.rpm link, and it was smooth sailing from there.
For others: just follow the link in @mentaljam’s comment and tap the noarch.rpm link, it’s quite a ways down the page below the blurb and screenshots.
Now the question is: what did I miss, and can you make it harder to miss? I was clearly supposed to know the bit about untrusted software, and I was supposed to know that the default browser has a handler for rpm files. Before your help I feared that I had to use the terminal and add the repo with zypper… I have no problems using a shell, but typing on the touchscreen makes me want to jump from a window…
About OpenRepos | OpenRepos.net — Community Repository System still links to https://openrepos.net/content/osetr/storeman .
Fixed, thank you for pointing!
Do you think Storeman Installer | OpenRepos.net — Community Repository System is the wrong place to mention the setting or even briefly describe the install process so newbies like myself don’t have to search the web for hints? Something like this would have given me all the answers I was looking for and this whole subthread would not exist:
To install Storeman Installer, enable “System → Security → Untrusted software” in the phone settings, visit this page using the phone’s browser, and tap the harbour-storeman-installer-$version.jolla_.noarch.rpm link further down the page.
I get it, I’m the first one to complain so what’s the issue, right? 
Could it be that I’m the first isolated newcomer in a long time, and all other installs are done by longtime users? I mean, Sailfish is not exactly a mainstream phone OS, I wouldn’t be surprised if 97+% of its users used it since Jolla 1 or earlier and the rest were their spouses, kids, and converted colleagues.
To add a bit more light from another angle: I do have some GNU/Linux knowledge; I wrote extensive tooling around zypper while I worked in SUSE and it still didn’t occur to me that the browser would default to installing the downloaded rpm. As I hinted earlier, I expected the installer to be in the official store, and when that turned out to be false and there was no info and the page includes run “devel-su pkcon refresh” in the terminal app, it seemed I was expected to type zypper ar https://repo.sailfishos.org/obs/home:/mentaljam/4.2.0.19_armv7hl/home:mentaljam.repo into the phone and that’s clearly ridiculous… Another reason I didn’t expect the rpm link to be the install procedure is that the OpenRepos webui I get on my XA2 with Sailfish 4.2 is clearly not meant for phones.
Long story short: it is not obvious (to everyone) and the fix is a short sentence, please add the blockquote above the the Storeman Install page, ok?
Anyway, thanks for the software, and your attitude. When I was researching what to install the contrast in approaches to users between the LineageOS XA2 port maintainer in XDA forums and your writing here and elsewhere drove me to Sailfish. They owe you a chunk of that 50EUR. 
OMG, “the computer” treats links to OpenRepos as spam and hides messages that include them. 
You are definitely right! I’m so used to using Sailfish that I didn’t think about newbies. I’ve added a section about installation process to OpenRepos. Thanks again for pointing such obvious things
Am I the only one with slow (it needs several minutes) opening Storeman when using the icon in the app grid? It happens on every try, not just the first after installation or reboot. If I execute the harbour-storeman in the terminal, it opens immediately. I can’t find something problematic in the /usr/share/applications/harbour-storeman.desktop file. The installation went smoothly and Storeman works fast after the opening process.
And one more. Looks like it can’t remember my login at OpenRepos even if I choose the save password option.
Removing and installing Storeman again doesn’t help.
I think someone has already complained about this. I have no idea about the reason…
It’s a known issue
Why Storeman or its installer is not available from F-Droid or APToide or UpToDown markets? For F-Droid would be enough adding a repo url.
I would guess because they are meant for apps for Android platform. As it states on F-Droid website:
I do agree it would be fantastic, if the installation process was as simple as installing apps from an app store.
Why should i use an Android App to install a SFOS application?
I’m sorry if I was being unclear. What I tried to express there was that it would be nice to use an app store (let’s say Jolla store or Chum) to install Storeman. I do understand why this is not possible at this point.
Storeman Installer available from Chum would really be fine, and I don’t understand where’s the difficulty here.
@robang74 Storeman is not available on F-Droid or Aptoide, because Storeman is a native SFOS app, therefore technically not possible on platforms for Android system.
Thanks for your clarification. Now, I fully got the meaning of the reply that @tuplasuhveli wrote and the counter question of @miau.
Therefore, I need to reformulate my initial question.
Why StoreMan, Chum and PatchManager are not listed in Jolla Market, at least after having bought the full license?
The same question should be extended to Micro-G suite.
I found the manual for installing Micro-G and sincerly, it is a bit long for something which is quite a basic requirement for almost the people want to use a licensed Android compatible smartphone.
A view above tehcnical stuff
It is ok that Sailfish OS would be a smartphone for hackers, but there is no reason that it would limited to hackers only, as long as Jolla prefers to sell devices instead of licenses.
The unit operative margin for every device can be higher than the unit operative margin for every license (I do not know) but the licensing market it easier and faster to expand and thus can be much more renumerative.
Why we should care about Jolla earnings? The day Jolla will go out of the market, our hacking here will probably reach a sad end.
Why we should care about Sailfish OS smooth adoption curve? Larger is the user base, more probably some people here got recruited for supporting that large user base.
Even, if you do not care about these two points, there is no reason to waste hackers time in something should be smoothly addressed by a decision. In fact, the day you would reinstall the SFOS on your own smartphone, the same tricky adventure will be repeated, necessarly.
The full (paid) licence is for the Android support and a few other things. (edit: word suggestions)
Storeman, Chum and Patch Manager is a completely different thing and has nothing to do with the paid SailfishOS licence. A free license also includes Storeman, Chum and Patch Manager, because this is an initiative of engaged coders and not Jolla stuff (in legal terms). It’s free and easy to install Storeman and Chum additional. See this like additionally installing F-Droid and Aptoide additional to Google/Android store on an Android phone.
Thanks for this clarification.
Refering about my previous post, I have updated it adding a A view above tehcnical stuff section.
The users can legally install some SFOS apps or even modify the system as they like without paying anything to Jolla. It is 100% ok for me, also.
On the Jolla side, they have a clear interest in offering with the paid license some other benefits like an easy way to install Storeman, Chum and Patch Manager and bla bla.
Are you an hacker user and your are fine living without Android support? Fine!
Are you a advanced user that wish to look outside the golden Google/Apple dualism? Pay per enjoying a smooth experience! 
I am more interested in the second point than in the first. The first is intriguing but it is slowing down my plan about SFOS adoption as a replacement for my Google Android smartphone.
Under this point of view - as advanced user - I reached the conclusion of having wasted my money and I need to go for an alternative smartphone/os pair.
(Un)fortunately, there is still alive a Spectrum 16K kid in me and here we are! 
Jolla Store is restricted in terms of APIs and therefore we don’t have those apps in Jolla store. The restrictions of Jolla store have been made in order to protect users from malicious software, but the consequences of this policy seem quite clear.
Some apps can be installed from various sources, but if installed from Jolla Store, they won’t have all the features they have in e.g. Chum. By the way, there is an old thread you might find helpful.
I believe this is something we all agree with. The current situation of the OS is a consequence of Jolla’s small developer team (around 30 members). If you want to contribute to the development of the OS, you could take part in the community meetings (propose topics or open PRs) and stay active on the forum. Of course, if you have the skills, app development is a great way to gain larger userbase!
EDIT: It is always nice to see new and active users on the forum, keep it up! Sometimes the feedback can be a bit harsh, but I find most people being nice and friendly to each other. 
Let me rephrase your statment to see if I understood it. Jolla Market does not allow to redistribute apps that use some API. Therefore, it exists a Sailfish OS apps framework that exports API. In this case,why having API that cannot be used for public apps? I wish to understand better this part.
Probably, it would be better to develop an app for configuring the smartphone after the first installation.
For licesed users, it could be something like this:
The post installation configurator can be delivered also with pre-installed smartphones that Jolla will sell. Other licesed users can download it from the Jolla repository. Some, configuration activities can be considered mandatory (M), others just suggested (S) and some others optional (O).
IMHO, 30 techies are not a team but an entire IT staff.
I was developing app for GNU/Linux when the GTK+ were at their 1.0 major release or a little below. The first italian article on that subject is mine and it brought me to my 2nd consultancy. Because I earned the 1st one when I have been catch shell-scripting on one of the University’s VAX servers by a vice-chief system administrator… 
In 22 years of IT career, 15 has been spent working as consultant. For this reason, I am used to deliver products/solutions. Some times, such products/solutions has been developed by myself but in most cases, my role was about integration rather than development. Consultants do not carry titles. We leave titles to our clients while we are focusing on make the things happens. Otherwise, I would be entitled as an experienced product/solution manager by now. 
I happily leave app developing stuff to the next generation nerds¹. Please, do not count me in as developer! 
¹ Java is the language of the future, we are saying and earing that since its debut… 
I’m not a developer and can’t give you a straight answer, but I hope you find this documentation helpful. Also, see API Checklist and Allowed APIs. There is an old thread, where Jolla was interested to hear developers’ thoughts on the store. Again, that thread might be helpful.
This topic is going a bit OT, so I would feel more comfortable continuing the conversation in another thread.