On the individual product page on the left hand side you will find PSD templates for each of the products.
To open a PSD template you need to have Adobe Photoshop installed on your computer.
Should you not have access to Adobe Photoshop you can easily create the template yourself. To do this you need to make a new page and set the dpi to 300. You need to make your page size the same as the print area you see on the product builder. This measurement is shown on each individual product builder. For example the print area on a ceramic mug is 200 x 90 mm.