Recording from Mixer to 13" Macbook Pro

Hey everybody,

First let me be frank, I don't know much about audio equipment/mixers etc., but I do know some. Anyway, I do a lot of remote high school play-by-play broadcasts using four separte external mics that run from my Yamaha MG102c mixer, back into my 13" Macbook Pro. The problem I seem to be having is figuring out how to get my computer to recognize the external source (Mixer), so that when I go to record my broadcast for future listening, I can just use garageband. Now, I know they make USB/Firewire mixers, but i had to do this on a budget. The cord I have that I thought would connect the mixer back to my mac is just a basic right and left 1/4" plug to 1/8" adapter that runs to the single headphone jack in my computer. I don't know if I am not using the correct line channels to get the audio that is coming from the mix back, but for some reason I continue to have trouble. Anyway, any help would be much appreciated.