1. Log in to the presentation PC. This is a separate computer from the auto cue PC.
2. Open the presentation you want displayed on screen.
This can be a PowerPoint, Google Slides, Prezi (etc), or even a still image. Anything you display full screen here will appear behind you when 'presentation PC' is selected as a background.
Please note: Make sure it is set to full screen to avoid a capturing any desktop or window borders.