You could go to the 'you have .. points'- button and the read 'about points'. There it states the folowing:

Points are given to you depending on your pics popularity (basically on how many visits your pics receive) and user actions on your pages. If members vote for your pics, you are given points directly.

Points are given to you for your own actions on the site - participation in public chat, writing comments on the public pics, voting for the pics, etc. Note that voting actually spend points, but you will be rewarded for this activity afterwards.

I hope this answers some of your questions. I suggest you read the entire text carefully again so you get a better picture about the point system.