How do the NFL playoffs work?

can sum1 explain it? i remember the colts had a good record in 07 or 06 i think and didnt even make it. raiders went 8-8 undefeated in division and didnt make it to wildcard, altho the seacocks did. jk bout seacocks lol. how do you make it to wildcard and division playoffs? and what are seeds? simple as possible?