How can I plaug my guitar into garage band? The employee at my local apple store told me to get a guitar cable, and on the other hend have a head phone plug in. Im not sure if this is correct, please help...
Yep. You need an adaptor. Get something which is 1/8" male (like headphones) and 1/4" female (to plug your guitar cable into). Then plug the 1/8" into your line-in jack and you're set. The online Apple store has a cable that does this for $20 but the $3 adaptor I bought at Radio Shack works just as well.
Your Guirtar has a mono, unpowerd 'hammer' jack
Just buy a converter to a mono headphone jack and plug it into the mic in port on the back of your mac.