The timer at the top of the screen marks the time of the audio track. Click about 10 seconds into your track. Notice the flashing line where you just clicked.

If you press return, the playhead will go back to the beginning of your piece.

Click the selector tool, and click just before the first bit of audio (you can tell where the sound is by looking at the patterns of the waveform.)

If you have extra sound at the beginning of your file that you want to trim off, click, hold and drag over the unwanted section.

Notice again the slip, shuffle and grid buttons above. The slip should be highlighted. Press the delete button and notice your selected audio has been deleted but nothing else in your track has moved. This is because you are in slip mode.

Undo this delete by pressing Cmd-Z.

Now click on shuffle in the upper-left hand corner and again hit the delete key. This time, the audio shuffles back to the beginning of the section you deleted.

Next, try clicking on the grabber (the hand icon) and dragging your audio around. Surprise, it doesn't move! That's because the slip key has to be active in order to "slip" your track along the timeline.