What do you mean by "start by creating a session?" I'm an architect(building designer) and a novice programmer trying to learn to use the tools to help in my design process. But I'm kinda stuck in trying to start the engine, let alone drive it. Any advice would be helpful!
How to use object Capture?
Take a look at the following article and sample code
https://developer.apple.com/documentation/realitykit/taking_pictures_for_3d_object_capture/
https://developer.apple.com/documentation/realitykit/creating_a_photogrammetry_command-line_app