First open Matterport Workshop and take some 2D Snapshots of your Matterport Space (not 360º Snapshots).
Your Highlight Reel is a simply a collection of 2D Snapshots at the bottom of the user interface.
When the user presses the play button at the bottom of the UI (i.e. starts the Guided Tour), Matterport automatically moves from 2D Snapshot to 2D Snapshot. At each 2D Snapshot, it pans a little to show that this is an immersive experience and not a simple slideshow.
Transitions between 2D Snapshots default to "slideshow" mode. This means they fade to black as shown below.
You can also set the transitions to be "walkthrough" as shown below.