Canned music, laughter, or applause on a television or radio programme has been recorded beforehand.
Setup
1.) When first opening GarageBand, you'll be prompted to start a new project. Choose "Empty Project" and click on "Choose" in the lower right corner.
2.) GarageBand initially needs a track to start with. I find the microphone track to be an easy first track. Choose it and the click "Create" in the lower right corner.
3.) The initial application screen looks like this, but there are several things we can change that might make things easier for you if you just want a way to layer/mix tracks.
4.) Start out by hiding the Library (clicking the button the red arrow is pointed at)
5.) The resulting screen should look like like this
6.) Next, it can be better to show a more detailed view of tracks. Click on the button indicated by the red arrow. If at any point you want to hide the editing part of the window, click on the scissors icon OR press "e" on the keyboard
7.) The resulting screen should look like this.
8.) There is a metronome function in GarageBand, but you probably don't need it when using tracks that will be imported vs making your own music from scratch. Click on the button indicated by the red arrow.
9.) The resulting screen should look like this.
10.) In the canned sets I create, I am more interested in the time of the sets than I am in the bars, beats, and tempo. To change the display to time, click on the region indicated with the arrow.
11.) Clicking there will reveal a pulldown menu. Pick "Time".
12.) We will probably want to make use of what GarageBand calls "automation." This allows you to define the volume of tracks as they fade in, out, or in custom defined patterns (covered later). From the menu item "Mix" select "Show Automation". The keyboard shortcut if you want to turn this on/off at anytime is "a".
13.) After all those steps, your setup should look something like this. Now you are ready to import audio tracks.
