When you have selected your product configuration, put your favourite product into your cart by choosing "order now'.
You can find all your products in your cart, by clicking on the shopping trolley icon on the right top in the menu.
You can add your design in the cart by editing the design of your product configuration of choice.
You have the possibility to:
Create your design with the Designtool
Upload your design with the Designtool and the file check
Edit layouts with Design tool when you have selected a layout
More information on designs can be found under "Start to design"