GarageBand '11: loop browser
Using the loop browser, you can quickly search for loops with the instrument, genre, and feeling you want, preview them, and add them to a project. The loop browser has three views: column view, button view, and podcast sounds view. You choose the view by clicking one of the view buttons in the upper-left corner of the loop browser. You can also customize the loop browser to suit your way of working. When you open the loop browser, it appears to the right of the timeline.
To open the loop browser, click the Loop Browser button (with the eye icon) in the control bar.