Once the video has been uploaded and processed, you can then add it to a collection's menu for it to be accessible to the viewer.
In the top bar, click "+ Video Button"
Select which videos you want to add to the current menu, then click "OK". You can toggle between viewing "All Videos" and "Collection Videos" (videos already referenced in the collection) at the top. You can also search for a specific video.
Tip: You can select all the videos contained within a project at once by selecting the project instead of the individual videos.
The videos have now been added to the menu as buttons. You can change the button names by clicking on them, or change the video start time and thumbnail in the button's settings.