Can someone explain to me how the Level system work?

I tried to find some info about that system, to fully understand how it works. I couldn't find anything really detailed about that on the F.A.Q. section and even while trying to find that info using google I can't get any real details about how it work.

I understand that the more you give, the more you get a higher level of course. But I'm looking for more details, if someone has the numbers in play and why some game worth less than other. It seems to have a special rule with the bundled game that gives less point, but other than that I'm totally lost.

Sorry if my English is bad, I'm not a native speaker.