Are you trying to do this in the Edit view? You really need to use the Multitrack view if you want to record overdubs. They can either be on separate tracks or stacked on the same track.
Well, I am in Multitrack view. If I were to re-record a portion of the "presentation" on a second track, could I then simply drag/drop it into the original recording?
Not sure what you mean about "stacked on the same track".
Do you know of a tutorial that focuses on these specific issues?
Thanks so much for your help.