Most of them have a membership list that you can add yourself, which is usually linked at the frontpage of the wikiproject and some you join by simply placing a banner such as the CVU one on your userpage.
As for other more advanced roles, such as rollerbacker or page reviewer, again all of those typically have the instructions on those respective pages, many of which will require you to first gain more experience in editing on Wikipedia and then if the permission is relevant for the type of editing you decided interests you, you can request them at WP:PERMS, which also has a listing of many common advanced permissions and the high level requirements.
Note that you don't necessarily need many advanced permissions to do a lot of useful things on Wikipedia, it just depends what area of editing sounds interesting to you.
In general, if you want to learn more and have more questions, you can check out the WP:TEAHOUSE, which serves as a forum for newcomers to ask questions on any topic around editing on Wikipedia. I also just posted a Welcome message on your User talk page with more helpful links to help you get started. Happy editing. Raladic (talk) 21:16, 11 August 2024 (UTC)Reply
Also want to point out that another important area of vandalism to look for is subtle/undetected vandalism, which can stick around much longer than new changes. I've written some about it but even just searching questionable words/phrases can turn a lot up. Gnomingstuff (talk) 05:49, 16 August 2024 (UTC)Reply
Latest comment: 3 days ago1 comment1 person in discussion
I don't log in to Wikipedia frequently enough to do this justice, so I thought I'd throw this out there in case someone else cares to. Zombo (singer) appears to be getting targeted by an IP-address vandal for "silly" (and tasteless/offensive, IMO) vandalism. Multiple edits have needed to be reverted in the past month. The last incident had "revert obvious vandalism" as the edit summary, muddying the water.
Bsammon (talk) 00:19, 22 August 2024 (UTC)Reply