If your car stereo has a mini-jack aux-input (should look exactly like your phone's headphone jack) then you just need a male-to-male audio patch cable. It'll have a headphone-type connector on both ends and shouldn't cost more than $10.
However, it sounds like your car lacks such a port, so things could get a bit more complicated. What sort of car/car stereo are you using? Once I know that, I can offer you a few suggestions.
I have an lg rumor which has a 2.5mm headphone jack. Im assuming i will have to get some sort of adapter but i dont know what kind of cable i need. The only place i see that i can plug anything in in my car is the cigarette lighter, but i have been looking online and cannot find anything. Any help is much appreciated.