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 "League Manager Tools" tab and click on "Assign League Manager Powers".
Full List of League Manager Powers
The full list of powers that a League Manager enjoys are as follows: