That’s what Getting Started with OH3: rewriting the tutorial - 1. Introduction is supposted to be. If you can contribute, even if by highlighting sections or passages that are not clear, please do so. They are wikis so you can edit them as well.
OP isn’t a brand new user though. He’s has some experience with OH 2.5 already. My answer was for him, not the generic new user. I’m ambivalent about truly new users. Selfishly, I’d like to get some truly new users to start “testing” the Getting Started tutorial. And even with the challenges with installation right now, I think that tutorial is already better than the OH 2 getting started tutorial (that was never finished) so in a lot of ways, the docs for OH 3 are even better than they currently are for OH 2, as incomplete as they may be right now. For references, the old OH 2 docs are still mostly if not completely valid.
I personally have been using OH 3 as if I were a new user. I’m not migrating my config to it, I’m recreating it on it. Everything that can be done in MainUI I’m doing through MainUI (and I’ve filed lots of issues as I go, most of which Yannick has been very quick to address 
). I’m even rewriting my rules as JavaScript though MainUI. And I have to say that the way that MainUI presents things and the stuff it does for you certainly pushes one to approach, think about, and implement the home automation in a different way. As a result, I fear that some users who are just getting started now will have a hard time moving to OH 3 later because the mental model that was built up of their configuration isn’t quite presented in the same way.
The semantic model is a really big part of that. If one approaches their config from the model first everything goes soooo smoothly. Things are discovered, we create equipment or points from the Thing and all the Item stuff and the UI stuff just happens. I’m not even going to port my sitemap over to OH 3, there is no need. Switching to that kind of approach is going to be hard for many users, especially us old timers. But it’s so worth it.