Pretty easy, actually. When you get started creating a tee, it defaults to the front of the shirt. You'll see the small images with the front and back of the shirt under the main image, and the front has a check mark by it -- before you start your design, point and click and check the back of the shirt and when you upload your image, that's where it'll go. Zazzle has excellent tutorials and info, just hit Help in the upper right of most of the pages when creating. Or just go on the forum here -- DT usually has all the answers somewhere, he even has a tutorial of his own here somewhere... or just scream loud enough in the forum and he'll probably show up.