I've played some games here. I don't understand what we're given points for?

just to show how the members are getting involved with chess.com

for example posting on a forum gives you a point, or posting a blog or something

This is the best explanation.

http://www.chess.com/forum/view/help-support/how-do-i-get-points 

 Thanks a lot! I've thought :))))) they're for brilliant playing