Play with other FOX users using the default league rules. Public leagues are the quickest way to get into the game.
Join an existing custom league created by another user. Most likely, you've been invited to join the league and have been provided a password by the commissioner.
Browse and search the list of custom leagues created by other users. Published leagues are custom leagues that have been opened to the public by the commissioner in order to fill the league. If you're looking for a particular type of league (i.e. NL-only leagues, leagues that use FAAB, etc.), this is the place for you.