How to add a photo to the back of a t-shirt design

I am trying to purchase a T-Shirt. I have my design for the front of the shirt, but I am having issues trying to add a picture to the back of the shirt. I am new to Adobe and I have limited experience with Express. Could someone please guide me on how to put a design on the fron and back of the T-Shirt?

Thank You in advance

Jim C.