Realbasic program example

I need a Realbasic (mac os) simple program that allows the user to choose a source folder, and a destination folder, and specify a filename. This program then needs execute a shell command to tar the source folder and place it in the destination folder. I am looking for help with this piece of code actually as I'm having difficulty figuring out how to do that myself. (THIS MUST BE A REALBASIC PROGRAM FOR MAC OSX)