Help with licenseing

Help with licenseing

Ok so I am a bit confused about licenseing. I plan on devleoping a PC game that I can legal sell so I want to get all my ducks in a row before I use something that might get my in trouble. And there is a ton of great art here that seems to be free to use in comerical projects by my understanding. 

Most of the CC stuff is made very easy to usnderstand thanks to pages like this

http://creativecommons.org/licenses/by-sa/3.0/

Something that confuses me is the share alike, would that mean my who game would have to be release under CCs as well? Or as long as I make the artwork availbe like in a file in the game files I should be fine right? 

Then theres the ones that also have the GPL 3.0, sometimes in addition to the CC. What does that mean?