The OG is pretty much the legal document that describes and explains everything you would need to know to perform your role correctly. It would include things like safety procedures, opening and closing procedures, emergency procedures, area familiarity among many many other things. It's like a one-stop shop for anything you would need to know about your job. Some areas are very OG heavy and require you to read it cover to cover and they tend to be the more safety critical roles while other areas might mention the OG but never have you actually read it during training. If you ever had a question about how you are supposed to do something, you would refer to the OG. Kind of like a CM's Bible lol