Looks like on top of your website is the "topics" and on the drop down you can go to the "all" https://piefed.social/communities and then you can join other sites communities etc. Surprised nobody really even answered this lol
and on the main page you have local / popular / all for feeds you can view too. It should have a "subscribed" so you can see the ones you are subscribed too, I don't have an account though so can't see
Haven't been on there in like 10 years, glad all of you finally saw the light. Sad it requires being forced off though.