You can add markers to your audio tracks to note a precise point at which you want to do an edit or to mark off a segment of audio you want to delete (by entering two markers to define the audio segment).
To set a marker, click on a point on your audio track and on the number pad to the right on our keyboard press the Enter key.
A dialog box will pop up with several marker options.
You can name your marker for future reference, then just accept the rest of the default settings and click on OK to set the marker.
A yellow marker will now appear over the track.
Once you've set a marker, you can move it to a different location in the Timeline by clicking on it and dragging it to a new point on the Timeline.
To modify a marker after making it, just double-click it.
That will give you access to the same dialog box options as when you first created it.