If you hover the mouse pointer in the upper right corner of the audio event it will change to a "quarter-circle" icon. When you see this, drag the mouse to the left. The farther you drag it, the longer the fade will be.
Hi Brain,
Easiest way is do it like you would fade out video. Grab the top right corner of the audio, and drag it to the left until you are satisfied. For more control, go to 'Insert' > 'Audio Envelopes' > 'Volume' and check that box. Then just double click on the blue line and drag your volume around to your hearts desire. :) Let us know if this helps. Cin