Recording multiple tracks

I have a problem, I am going from a BR600 multitrack machine, I need to record in Audacity a bass, a percussion track, guitar, and vocal track, they all have to start at the same time, I have to export them to an email address as an attachment. I need a way to have them start at the same time, so that the recording engineer in Nashville can mix them and send them back to me mastered.

BR600 multitrack machine

Actually, it’s listed as a multitrack recorder. If you already have the music files on an SD card, where does Audacity come into it?