How do you create a soccer league?

You would need to:

Find enough teams or people willing to organize them.

Write rules for team membership and players elegibility
-Home teams provide ball and goals
-Player age limits?
-Professional or amatur?
-Entrance fee splits?
-Dues paid to the league

Create a schedule of games at fields verified to be available at that time.

Appoint or hire officials and make sure you have all of the games on the schedule covered.

Make league logos and promo material.