What should I do about my first day at work?

I'm 15 and I have my first day of work tomorrow at Coles. I don't know if they have that in America but it's basically just a place to shop for food mostly.. Anyways, I have the introductory day tomorrow which goes from 9am until 2pm and I'm just wondering what I should do so that I'm not all nervous and stuff.. =S I'm usually pretty confident but I don't know, I just don't want to mess up or anything haha..Any tips or anything?