Noob ques: Best way to output Garageband midi

Can I just click 'play' on the garageband software?
Can I just hook up my macbook's headphone jack to a PA system?
You could, but do you want to be dragging your computer to gigs? (Laptops are more easily stolen than guitars...)

Will Garageband export to MP3 or some other audio format? (I'm not a MAC kinda guy, so I don't know)

If I was planning on gigging with your backing track, I think I'd put it on an MP3 player or burn it to CD.
I'd rather hook up one of those to the PA, than taking my computer to a gig.

Hello,
I downloaded a few midi files and imported them to Garageband. I tweaked the sounds using different instruments available on garageband and turned off others to get the sound I want.

I'd like to use my creation as a backing track when I play acoustically (guitar) with a vocalist.

Do I need a midi keyboard controller? or Can I just click 'play' on the garageband software?

Can I just hook up my macbook's headphone jack to a PA system?

As you can tell, I'm still very wet behind the ears. I've read some articles on what a MIDI controller is but I 'think' garageband is all I need to connect it with some sort of speaker system for a live performance.

Please and thank you for any comments / advice.

Probably the best way is to export to a wav or other lossless audio format (flac, aac) and hook an iPod or CD player into a PA. Mp3s will sometime have subtle timing errors due to the lossy compression. They might not be much of a problem for live performance, but can wreak havoc when recording or trying to overdub onto the track.