In the first instance we would recommend our user guide as your first point of call for getting to know MDAnalysis:
https://userguide.mdanalysis.org/stable/index.html. The user guide includes a section on how to contribute to the project. We also have several issues on our GitHub repository labelled as "difficulty-easy" and "good-first-issue" which you may have to have a look at as good first time issues.
For questions about the project we would suggest posting on the MDAnalysis discussion (if it is usage based) or developer (if it is about contributing) mailing lists (see our GitHub page for links to both). We also have a Discord sever, see here for more details:
https://www.mdanalysis.org/#participating.