On this page you can customize your league by first creating division and then adding clans to them. Players do not necessarily need to be in the clan to play for that team, it's more of a means of organization.
TemplatesOn the template tab you can input the templates and team sizes for them. Every clan in every division will play round-robin tournaments (2 games max) for every template that you decide.
Once you're done setting up the league, click the "Finalize Divisions/Templates" button above which will then finalize clans/divisions/templates and you will be able to manually select which players play in which tournaments.