You and people in your league pick players from a "draft" to be on your team. Then you pick who you want to play. Teams are then split up into a schedule and each team plays each other. On game day, as the real life person plays, you earn points depending on their real life performance. (For example if your play throw 2 TD you get 18pts) At the end of the week, the team with the highest score in each match wins. About 3 weeks before the end of the regular season playoffs begins (best teams play each other)
Overall its pretty much you pick the players you want and pretend their on your team