score

Hi I am new here and provisional, I just won the last game I played, but my rating went down after, could somebody please explain why?

Somewhere in the FAQ there's a full explanation of ratings calculation. Your rating is p1200 until 5 rated games, from there on your rating is an average of the ratings of your opponents until you reach 20 rated games and lose the p rating prefix.

FAQ even says "your rating may go down even if you win a game". The whole FAQ is very detailed and easy to read, and it's worth a visit.