Playoffs happens after the last schedule game. If you are 2nd in your league you will play 3rd from your conference. If you win then you will play in the conference final against the winner of 1st vs 4th. If you win that, you will play in the league finals against the winner from the other conference.
If you win the playoffs you will promote to a higher division. i.e division 4 (as you are division 5 right now). If you fail to promote, then you will stay in your current league next season