Welcome to Lemmy!
I found that a large number of communities have been named after popular, and less popular, subreddits. So I found them easy to find. There was an old r/Redditalternatives post that has a decent range of communities to start out, which I've copied below. It is similar to the default subreddits.:
*Note:*The "World" hyperlink takes you to the Lemmy.World communitiy.
General
- Asklemmy (ee, world)
- Showerthoughts (ee, world)
- General discussions (ee, world)
- Mildly Infuriating (ee, world)
- You Should Know (ee, world)
- No Stupid Questions (ee, world)
- Mildly Interesting (ee, world)
- Memes (ee, world)
- Lemmy Shitpost (ee, world)
- Videos (ee, world)
News/Politics
Pets and such
Gaming
TV and Music
Pics and Art
Technology and Science
- Technology (ee, world)
- Science (ee, world)
- Fediverse (ee, world)
- Android (ee, world)
- Hardware (ee, world)
- Privacy Guides (ee, world)
Sports
Others