If you are in a Standard League, your League Manager is the person who sets up your league every year and determines league logistics such as the following:
The scoring format
A suitable draft type/date
Inviting friends to join the league
A more advanced version is League Manager Leagues. League Manager Leagues allow League Managers to customize their leagues down to the smallest detail. If a League Manager ever wants to relinquish their role within a League Manager League, all they have to do is navigate to the "LM Tools" tab and click on "Assign League Manager Powers".