Now that all of that is out of the way, we can move on to actually doing things.
There is no real categorisation of what you can do, so take a brief look at the introduction of any articles that interest you in the next section. It will list any alternatives that you might want to pursue instead. For example, Radicale vs NextCloud: Radicale lets users sync contacts and calenders, while NextCloud let's users do that plus an enormous number of other things but requires more resources (both on the server and on you).
The CHANGELOG in the appendix is useful to keep track of updates to this book that you may want to apply to your own server. However, it does not currently exist because the author is bad.