How to Activate new iPhone 4s?

So I got an iPhone 4s today and the people at the store told me I could easily activate it myself. So I brought it home to figure out. I'm upgrading from a basic phone (Samsung Reality) and my plan is upgraded too, but I can't seem to figure out how to transfer the phone number and get service on my iPhone! Like, I can still call people and text on my basic phone, and I can't on my iPhone. How do I transfer the number and the service? Please help!

Added (1). They did say they could activate it for me, but I asked if I could do it myself as I was in a hurry to get home.

And here I thought the AppleBots crowed about how EASY it is to use an iPhone. You paid heaps of money and they want you to activate it YOURSELF? So much for the great customer care from Apple… Lol

Call the carrier. Their phone, their network. They're supposed to help you. That's what you pay them for, right?