Reels can be considered as movies. They contain the path to a movie file.
Reels can also point to an audio file that can be displayed in the timeline.
They can also point to a background image, to be displayed in the monitor. This image can help to find the best position for the text.
A reels track may contain several reels, but only one reel can be active at the same time. The active one will be displayed in the monitor.
To make a reel active, display its context menu and select "use".
Reels may contain additional information, for example, recalibration points and scene changes.