Bagging groceries advice?

I have a job as a courtesy clerk but its my first day and im a little nervous.How do you bag groceries? I heard you put boxes to form the wall of the bag then you put cans or drinks in the middle then you put another box on top of the cans and then you put the soft stuff in the middle? And what about the people who get mad if you use plastic instead of paper? Idk,but im kinda nervous and times at the groceries store can get busy and I want to be fast but I dont wanna mess up! Any advice much appreciated!