How does Riot choose which teams will compete in LCS/Esports?

I know it's a noob question, but I've always been confused on how all of this works. Say you want to compete with the pros, what do you need to do? Sign-up (with a team) for a certain tournament or do they choose the top 10 ranked teams from each server? I'm completely lost as to how this process works. Any insight would be very much appreciated, thanks.