It's based on the NFL, obviously and you draft players and every week they play. The players give u points for how well they do and the person with highest points each week wins. At the end of the year there are playoffs with the 4 highest win total teams and they face off until the champion is decided.
EDIT: are you guys able to join without me inviting you? If not email me your email you used to register on nfl.com and I will invite you