It’s pretty simple.

1. Lemmy is a collection of topic-based communities.
2. People share what they find interesting to the appropriate community.
3. People who subscribe to the community vote up posts that are on topic and vote down posts that aren’t. They can also leave a comment to discuss the submission.
4. Posts are sorted by votes/comments so that people see popular ones.

Have fun and participate as much or as little as you want.