Virtual Cameras represent the views into the virtual experience that are configured in MixCast, and so are a crucial component to creating nearly any form of immersive video. They also are where you can configure the mixing of a Video Input with the virtual view to create a mixed reality video feed (also called compositing).
The first aspect to consider is whether you’re wanting to capture a view that is comprised only of the virtual experience, or one with a mix of virtual and real views (mixed reality video). If you’re mixing virtual and real views, check out the Compositing page. If just capturing a virtual view, read up on how to assign its location on the Tracking page.