@haemogoblin Yes, it works exactly like that by default for libretro emulators Select and Start exits to the menu. To begin, you should read this https://retropie.org.uk/forum/topic/3/read-this-first and provide info on your setup quickly followed by https://github.com/retropie/retropie-setup/wiki/First-Installation#configure-controllers which explains everything you are asking.

@herb_fargus lol. Found a half a beetle. When i was a kid i opened a snack size dole can of mixed fruit and it was just water and rocks. They didnt even give me mixed rocks....
My ex wifes ex husband got a back of doritos and it had a beetle that was coated in the cheese powder and deep fried. It was pretty gross seeing the pics.