Also, some stores are now unloading trucks at 7:30am. If it's an especially low volume store, expect to be on the line while the truck is getting unloaded. If they want to be nice to you, they'll put you towards the back (or end) of the line so you can get accustomed to how the process works. If they don't, I suggest requesting to be. It can be intimidating at first, but you get the hang of it real quick.
You'll basically be in charge of three pallets that are for its respected departments. You'll see a sign hanging from the steel or ceiling that tells you which department number belongs to which pallet. All you do is check each box on the conveyor belt for your department numbers and if they don't belong to you, keep on pushing them down. Stack your boxes from the back of the pallet and going towards you. If you stack your boxes nicely, your pallet pullers will love you.
And if you're not working the truck, like what the guys said above, you'll just be working on pulls. Grab a tub, flat, or tier cart that has a green pull sign on it and start stocking. Good luck. :]