GarageBand 3 comes with a wide array of jingles and sound effects to make your podcast pop. To add an intro, outro or sound effect:

1. Click the eye icon
to open the Browser.
2. Select a category, like Jingles,
and then choose from the subcategories.
3. Click on a sound’s name to hear a sample.
4. When you’ve found the correct sound, click its name and drag it to the Jingles track in GarageBand.
5. Let go and the Jingle track will render. You may need to slide your audio tracks around to accommodate the new addition.
Ducking
It may be necessary to lower the volume of backing tracks to more easily hear the spoken narration or dialogue. Lowering the volume of some tracks to make others easier to hear is called "ducking." GarageBand 3 automatically gives your vocal tracks priority to any underlying sound effects. However, you may want to change the order of ducking if you have two vocal tracks or need a sound effect to stand out.

You can apply ducking to any Real or Software Instrument track
1. Select Control > Ducking. A ducking control, upward facing and downward facing arrows, appears in each track's header.
2. Click the downward pointing arrow on each track you want to make a backing track
3. Click the upward facing arrow on the tracks you want to give priority.
4. Choose Track > Show Track Info. In the Track Info pane, click the Details triangle.
5. Drag the Ducking Amount slider to adjust the amount of ducking.
Note: To disable ducking, deselect the Ducking Amount checkbox.