To create a product:
Choose a product
Open its Design Lab
Upload your artwork
Adjust placement and scale
Cover the template fully and avoid red areas
Choose products options if necessary such as thread color and fabric type.
Use the 3D preview to check your design
Save your design
Once you save and close the Design Lab session, the design cannot be edited. So it's best to make sure you are happy with the product before navigating away from the Design Lab. As long as you create an account, all designs you create will be saved.