how to wire in a 2 line output converter

i bought my wife a sound system for her pontiac g6 gt 2007 but in order to hook it up to the factory stereo i need to wire up a 2 line out put coverter and i have no i dea what i am doing i need to figure out what each wire means on the factory audio wiring harness you know the the one that plugs into the factory stereo then i need to figure out which wire is the right speaker output and the left speaker output if there is anyone out there that can help me i would greatly appreciate itjared mcelderry