Anyway, you don't join a project - there's no membership list, and there's nobody who will tell you do this or do that or whatever.
What you do is get on the forums (usually mailing lists, IRC, and bug tracker), start following the discussions, and help out where help appears to be needed. That's it.
If you wait for hand-holding or permission you won't get anything done. You have to be persistent and just start doing stuff.