In my last game i had 1491 points. I have won 13 points and have now 1500. Someone can explain to me?
You won 13 points on your blitz rating (1491+13=1504).
Your standard rating does'nt change with the same amount as it is a wieghted average on the three time controls.
For further info and insights about a possible future ranking system, it's being discussed here :
http://fr.lichess.org/forum/lichess-feedback/my-opinion-of-the-new-rating-system