Just because the NFL regular season is over doesn't mean your fantasy football season has ended. Playoff pools keep the fun going throughout the NFL postseason, and give you an extended schedule of sorts.
While roster sizes and rules tend to vary, the format is usually standard in that you draft a roster of players who have made the playoffs, and enter a lineup each week during the NFL postseason. Your players accumulate points only for games in which they actually play. Rather than going head-to-head against other opponents, the team with the most points at the end of the NFL playoffs wins the pool.
Since there is a limited number of players available, a standard-size fantasy roster is recommended, consisting usually of 1 QB, 2 RBs, 2 WRs, 1 TE, 1 K and a D/ST. Of course, you want to draft players who will compete in the most games possible, but that can be quite a challenge. The two highest seeds in each conference are guaranteed to miss a week because of byes, and the odds of a wild-card team advancing to the Super Bowl can be long indeed.