Think of gaming communities as clubs. They're big groups of people that get together for events, meeting new people, and tournaments.
Tournament communities
As states, these communities run tournaments for League players. They're usually the biggest (especially in league). Most run tournaments for profit.
Multi-gaming communities
They have clans and events throughout a variety of video games. I think these communities have the most variety in what entertainment they offer for their members.
Casual communities
Usually run unprofessionally. They don't run tournaments or have a strict code. They're usually just for social purposes where you can meet new people. Like a hangout spot or something.
Obviously this doesn't cover every single community. Each one is different but they have a similar structure. If you want to be a part of something then I recommend you join one.