Dolly, I think the actual formula is in wikipedia, but basically the amount of points for a win, loss or draw are based on how far apart two players are in rating points. So if you beat a player rated way below you, you gain very little, but if you beat a player rated way above you your rating jumps. It is based on a mathematic formula, so the ratings of the two players determines the points at stake. Note that during a game you can see this under the "details" tab if you click "show rating adjustment."
Rating Points

Thank you for that! Now it makes sense..! I did beat a couple of people with greater ratings and my score jumped significantly! I will watch it from now on... Dolly

Another factor that determines how large your rating changes are is how many games you've played. Someone who is new to chess.com and has only a few games may have a larger rating change for a particular game outcome than a more established (more games recorded) player would get for the exact same game outcome. When you're first starting out you can get some pretty big swings up and down for a little while.
--Cystem

Thanks for your comment. I played many unrated, and now regret it, as it would have improved my scores...I just havent played enough but am learning with every game... Dolly

Chess.com uses the Glicko system with a logistics distribution. Glickman's paper on it can be found here: http://math.bu.edu/people/mg/glicko/glicko.doc/glicko.html
Chess.com's explanation of their use of it is here:http://www.chess.com/article/view/chess-ratings---how-they-work
Hello Everyone!
Can someone please explain to me how points are established? It seems to me, that is varies so greatly when I gain or lose? I would appreciate someone's input to enlighten me. Can we set them ourselves? Thanks for your input. Miss Dolly in Calif