Righto, your orientation is essentially the health and safety basics of working for the company. A local manager will conduct it and when i did mine (all be it 4 years ago now) we had to complete a few safety forms, fitness to work etc.
From what i now gather you will be shown a DVD with a little bit of company info to get you better antiquated with the job.
Take your bank details, national insurance card (do you have one of you arent 16?), references along with you as im pretty sure they will need copies for store records.
Mine probably lasted around half an hour, pretty informal, and a good opportunity to ask someone fairly knowledgeable about any questions or problems you have.
Hope this helps
Matt