When you connect a second monitor or a projector to your Mac you will want to extend your desktop as opposed to mirroring your desktop. Extending your desktop allows you to place a separate presentation window on the second monitor while keeping the TrialPad interface on your primary monitor.
Details on connecting multiple displays can be found here:
Details on the settings to select can be found here:
Then in TrialPad, when you click the Output switch to On an empty presentation window will appear ready to display your evidence. You can move this presentation window to a secondary monitor by dragging the window by the top bar (just to the right of the red/yellow/green “traffic light” window buttons), and then have the presentation window fill the screen of the secondary monitor by clicking on the green window button. Once the presentation window fills the screen the traffic light buttons will disappear but you can view these buttons again, and bring the window back to the original size, by moving your mouse to the top area of the window to reveal the traffic light buttons again and clicking on the green window button. A faster way to maximize the presentation window, and then bring it back to its original size, is to use the keyboard shortcut FN (Globe) + F.