The background is only for preview. Exports are transparent and pinned to the bottom of a 1920×1080 frame, so they line up when dropped over your video at full size.
Drop to add to the Library
Shots
Not linked to OBS
Click a shot to lock it on screen; it stays until you click it again (or Auto), then switching goes back to automatic.
On air
Cameras in OBS
Live thumbnails
See which camera is pointed at whom, then assign them under Hosts on the right.
Rundown
Not linked to OBS
Click a scene to cut to it with OBS's transition. → / ← (or Next in the top bar) step through the show.