There are two ways to rate pictures. Firstly, you can actually go into someone's album through their profile, pull up a picture and use the voting tab. The other way is to use the rating tab to vote on a random picture or profile.

The lower line shows how many people have rated your picture using the random selection. The stars are how highly they rated it. The top line shows people who have actually clicked on your picture and rated it, and again the stars show roughly what score it has achieved.

I hope that helps.

Night xx