The Short Answer: You either create a new league and invite friends to join, or you join an existing league using a League ID someone shared with you.
When you finish creating your account, you'll see a simple choice:
Most managers join leagues with friends, coworkers, or online communities. The game is designed around private leagues where you know (or get to know) your competition.
Create a league if:
Step 1: Tap "Create a League"
From the "Do you have a league?" screen, select the create option.
Step 2: Name Your League
Enter a name for your league. This is what all managers will see.
Examples: