How To Add Volume And Pan Fades On Sounds
Let's fade out a sound.  Normally, you could do this by dragging the envelope points around, adding new points and shaping the fade out manually.  However, there is a built in way to make a fade.

Make A Selection
Make a selection on the area of the sound you'd like to fade out.

Make A Fade
Now push Alt+2 to fade it out and it creates the following:

You can also create a fade out by clicking the Sound menu, followed by clicking Fade Out, followed by clicking Fast, Medium or Slow.  

Fading Pan, Low Pass or High Pass Filters
You can also fade in and fade out the other envelope types by choosing the correct envelope type on the toolbar and then using the fade in or fade out commands.  Choose from pan, low pass filter, low pass resonance, high pass filter and high pass resonance on the toolbar.

Keyboard Shortcuts
The keyboard shortcuts are designed so that you can use the mouse to make selections with one hand and with the hand use the keyboard to fade in or out.  Simply hold down the Alt key, make your selections and push either 1 or 2 for either a fast fade in or fade out.

Here are the actual keystrokes that correspond to the fade types.

Alt+1 Fade in fast
Alt+2 Fade out fast
Alt+3 Fade in medium
Alt+4 Fade out medium
Alt+5 Fade in slow
Alt+6 Fade out slow