On either the specific guitar track, or on the main fader, right click the fader and select "Edit Volume Automation". That will open a volume envelope, and you can draw in the fader from there. Using the arrow tool, you can click a point for the fade to be at full volume, then click another point where the fade will start/end and drag the line up or down (fade in/fade out). Then between the 2 points you will see a dote that will let you design the curve of the fade.
See Automation in the manual for more detailed information.