Hi there,

if you look on the audio track you should see a horizontal line disecting it with small rectangles. If you place the cursor on the box on the very left, depress the left mouse button, and then slide it to the right, you will have created  a fade in. Doing the opposite on the right hand side will create a fade out for you. However, make sure that you have 'ungrouped' the audio and video track, or you will fade both.

Have fun.

M o' L