Hey guys i joined Seasonal ladder yesterday, played my first game, the map is really good but as i noticed i won my first game and i checked my points afterwards i had 1645 (and the other guys first game) and he had 1686, now i dont understand why he has been given more points for this even though he has lost.

You get, in addition to the result of the game, a fixed number of points for every game you play to avoid people gaming the system. Since he has 2 games more, this makes up for the difference.

You get those points even before the games have finished?

no i got them after the game finished, but Math Wolf i still don't really understand why

Sorry, that was in regards to the fact that your opponent is currently playing two more games, but neither of them has finished.

Poor C-17. He's won all his games to this point, but 3 of the players dropped already so his rating is still lower than mine, despite beating me :P

Your opponent is currently playing in 2 games, and have finished the game against you. Thus total games for him is 3.
Your total game number is 1, (as you are currently not playing in any games).

You get points based on total number of games. So even though you won, the extra points he gets from total games makes up for that with respect to the points.

I basically just rephrased what math wolf said, hope it is more clear for you :)

@Beren
"The rankings are determined using the same ELO scale that the existing ladders use, with one small modification. Players who play fewer than 20 games (due to leaving the ladder early or joining late) get a penalty of 40 rating points per game. It’s best to join the season before it starts and stay in it for the whole 60 days to ensure you do not receive a penalty. The penalty exists to ensure players can't game the system by intentionally joining the season late and riding to a high-rank by getting a few lucky games."
-Wiki,
I'd assume the penalty is removed once you create the game.