You can always read about how the Apple II was used in development of VCS games, but that's about as much as you learn.
So how did Atari use it? Did they simulate the TIA on it? Was there any direct electrical connection between the Apple II and the VCS? Maybe they just used the Apple II as a terminal or storage device.. Or maybe to test and trace 6502/6507 code?
Maybe they just used it as a utility computer, to convert hex/dec and build up playfields and charts and sprites and stuff like that.
Though I can't imagine the Apple II producing anything as colorful or "soundful" as a VCS game - the Apple II somehow played an important part in writing VCS software back in the day. What was that role?