The NFL has been slowing expanding the playoffs for years. What started out as 5 teams from each Conference is now 7.
So you have the 4 Division Winners. They get a home game no matter what. So even though the Ravens & Chargers & will finish with a better record that the winner of the AFC South, they will still go on the road.
The first weekend of the Playoffs is the Wild Card Weekend. In the old days, the WC teams played each other for a slot in the main draw. But now the 3 WC's play the #2 - #4 Seeds. The #1 teams gets a week off. So after this weekend, there are 4 teams left in each Conference. That is why the #1 seed is so important. Gives the guys a week to rest and heal up a bit.
The second weekend is know as the Divisional Round. The 3 winners from the WC round and the #1 Seed then play with the 2 highest seeds getting home games. Unlike the NBA, the NFL reseeds the Playoffs weekly.
The third weekend is the Conference Championships. The two remaining teams play at the higher seeded team for a chance to go to the Superbowl.
Clear as mud now, right?