Join a Head-to-Head League and square off weekly against other managers. Each manager sets his/her lineup based on league requirements and is matched up each week against another manager according to the league's schedule. Whoever accumulates the most fantasy points -- based on your league settings -- wins the game. Weekly results are then tallied into an overall record.
In non-playoff leagues, the team with the best winning percentage wins the championship. In playoff leagues, the top teams have an elimination tournament to determine a winner.
Join a Points League and simply set your goal on being the highest scorer. Set a weekly lineup based on league requirements and hope your players collect more fantasy points than anyone else's. Points are tallied throughout the football season, and the team with the highest total at the end of the year wins the league championship.