A four wire cable is one that has four wires in it. Usually a red, black, blue and a white wire. When talking about cables the ground wire is never counted because now a days all cable sets have...
I recommend no smaller than 8 gage wire. 6 gage or 4 gage if you want a professional type cable. The bigger the wire the better, but the more it weighs. 8 gage is sufficient for most people.