How do I record in garageband with backing track

Hi All
I am blessed with a new 2013 iMac and an Apogee Duet 2 and a guitar.
Now I have purchased some backing tracks over the years.
i like to play 60s instrumental stuff like The Ventures or the British Shadows songs..
Now how could I get a backing track into garageband and then add my own guitar playing to that recording??
Anyone got a step by step maybe??would be really grateful for any help.

All my backing tracks are in the mp3 format...so do I need to download some plug-in to garageband maybe??like lame or??

anyway hoping for help..
best regrads micael

 

Hi Jessica and thanks for your reply.
And no I am toatlly new to garageband..and actually to Apple and OS X as well...but so far very happy with the switch from PC on a personal basis..
Since I work with coputers and have dome so for some 20 years I guess I will always use PC at work.

Anyway I did actually try before posting this to select the mp3 backing from the finder and asked it to be opened by Garageband. But then Garageband replied that it can not handle mp3 files...
However maybe drag and drop makes Garageband work it differently..
I will try again this evening.
I will also look into the links you sent so great to get them.
Again many thanks.
best regards micael