^ Your answer isn't completely correct.
Here's how it goes:
Whenever you're playing on a team( ranked or not )everyone on the team that wins gets 1 exp. point. Whenever you're by yourself aka FFA ( Lonewolves or Rumble Pit etc. ) the people in the top half get one exp. point. So if there's 6 people in an FFA match, only the people that finish in either 1st 2nd or 3rd would get an exp. point.
Now as for skill:
Skill only applies to ranked playlists. NOT SOCIAL.
First of all, the more you lose, the harder it is to go up. So if you have played like 500 games in Team Doubles and you're only like a 30, it's gonna take a whole bunch of wins to move up.
When you're playing Lonewolves, you almost always go up one skill level if you finish in 1st. The same goes for second place. Sometimes it takes a few victories. 3rd place is kinda tricky. If you came 1st in a game, then 2nd in the next, and 3rd in the last one, you'll probably go up. But if you got 3nd, then like 6th, and then 3rd again, chances are you're gonna go down. 4th,5th,and 6th work the same way, but the chances of going down are greater.
For ranked
team games:
Generally if you win, you go up. Keep in mind that if you have lost a lot in a certain playlist, it's harder to go up.
You cannot earn exp. or skill by playing custom games.