If you're in a Standard League your commish is basically just the person who sets up your league every year. They'll choose the scoring format (anyone who is losing will eventually blame this as the reason for their failure), find a suitable draft type/date and then of course, they'll invite all of your buddies to join in on the fun.
The more advanced version is the LM League, the glorious format that we've all come to know and love where commissioners can tweak almost every detail imaginable in a never ending quest to create the greatest league of all-time. If you're a serious Fantasy Football fanatic then this is the option for you. And, if the commish ever wishes to relinquish the awesome power that the name carries, however foolish it is to do so, all they have to do is navigate to the "LM Tools" tab and click on "Assign League Manager Powers".