Cropping Screen Simulation

I had to keep redoing a screen simulation that has audio, and finally decided it was too time consuming to keep resizing the marquee around the recorded software, etc. (if there is a way to lock the size and position of the recording area between retakes and new recordings, please advise). So, I just decided to keep going and then crop out the portions that contained mistakes  after I was done recording.

I left a few seconds of silence after each mistake so I would know from the audio flat line that the area immediately in front of it needed to be cropped. I thought a visual cue would simplify the process. However, I don't see the audio bar on the Timeline. In fact, there is NOTHING on the timeline so I have no idea where to crop things. I clicked around and nothing seems to display the timeline items I typically see in a PowerPoint imported file.

How do I proceed? Thanks