Hello and welcome @Andreas_Jakobik 
As a self-hoster, you would need to install most of the plugins you want to use. There are some that come bundled with the core installation (like Chat, Footnote, Spoiler, Checklist, and others), but most would need to be added if you wanted them.
The website has a selection, but the full list of our official plugins can be found here https://meta.discourse.org/tags/c/plugin/22/official 
And the bonus to being self-hosted means that you can also install third-party plugins if you like as well, like the ones from pavilion https://meta.discourse.org/tags/c/plugin/22/pavilion 
I think there a lot of useful ones, but Solved, Assign, and Data Explorer are probably top of the list.