Need To Add Vocals To Instrumental, simple but how on a mac Options

[gdogg]

I got imac 0s10 g4 and garageband and itunes. I'm completely new to mac but I have a friend who has a mixer and I have acess to a akg condenser mic and was wondering if I can simply hook up the mixer and mic to the mac and start some kind of software program that'll let me click add track, add the instrumental, than allow me to click record-start recording my vocals thru tha micraphone and mixer as necessary over the instrumental on track1. than export it to mp3. A similar tool on tha pc is acoustica. please help, I heard I can save money by doing this, because I was gonna go to a big studio. I'm also not that fluent with appz like soundforge and protools, cuz it looks too confusing sometimes. holla back and thanks in advance.