There are 5 playable leagues:
American Superliague - 20 teams
American First League - 20 teams
American Second League - 20 teams
American Third League - 22 teams
American Amateur League - 22 teams
US Cup (FA Cup)
Pizza Hut Shield (Super Cup)
McDonalds Cup (League Cup for Superleague teams only)
Step 1Move the .fmf file in your editor data folder:
\Documents\Sports Interactive\Football Manager 2015\editor data
Create the "editor data" folder if it doesn't exist.
Step 2Start a new career game (won't work with classic mode).
A little pop-up window will come up that says there is X enabled editor files. Click OK.