Thanks for your response!
So I would start writing the stuff... but I'm afraid it would be then limited to the functions that I'm using for my site, and of course some explanations depend on the theme that I'm using
How can I make online users widget just like the one on the Categories page of this forum? The one on the right with round avatars.
It is a standard widget that comes with nodebb, you will need to run latest master though or wait for the next release.