In the basic version of START7, you can create a league or join a league. To join (or create) more leagues, you have to get the premium version of START7 for 1.99 €/month or 17.99 €/year. Then you can play in 10 leagues at the same time.
After the 30-day premium trial membership has expired, you automatically switch to the basic subscription. You can decide in which league you want to continue playing.