Deleting
Two actions remove material rather than replacing it. Both use the source markers to say what to remove, so set SOURCE-IN and SOURCE-OUT first. If either is missing you will see "Please use SOURCE-IN and SOURCE-OUT markers".
Delete With Ripple
Removes everything between the source markers, on every track, and closes the gap by moving the later material earlier, with a crossfade at the join. Use it to take out a cough, a repeat or a false start so the music simply carries on.
Delete Leaving Silence
Removes the same material but leaves the gap where it was, so nothing else moves. Use it when timing must be preserved, for example while working on a section that is aligned to something else.
A tip for slivers
After many rounds of zoomed-out editing it is easy to leave small, unwanted leftover pieces of earlier edits (slivers). Before an edit or a delete, ReaEdit clears slivers that sit right next to your markers so the join is clean, and tells you what it removed ("Removed sliver edit(s)"). It does not touch anything further away, so look at long projects occasionally.