Option W turn on Clip Overlay
P turns on pen tool
Add four points close to each other by clicking once for each point to one track (affects both tracks if they are stereo)
Hold the A key down (reselects the selection tool) and then Drag the line down between the middle two points.
It fades out and then fades back up. Timing is determined by how far apart you make each keyframe point. If it is a tight transition (quick fade down nad then right back up, then only three points are needed. Click for two points with space in between (points 1 and 3) then add point 2 in the middle and hold the mouse button down to drag that point down. It will fade out and then back in quickly.
I use Show Audio Waveforms to see quiet areas to apply the fades. I also use Add edit (Control V) and drag some space in between the clips. Then just right click to Add default transition to the out and in of each new clip in the usual way of crossfades. Make your own new default settings if they are different and used a lot. Such as 2 second crossfades or four seconds. Whatever works.
Gary