When selecting Digital Prints or Enlargements you can choose a Matte or Glossy finish. After you have selected your images to work with you will be presented with the screen below showing your images as 4"x6" Glossy Prints. To select different sizes or choose between Matte and Glossy finish you can either spin the carousel left or right by clicking on more sizes until you find the size and surface you require or click on the Quick Size Selection drop down menu on the right and select the size and surface finish.
Once you have found your desired size and surface you can start selecting your images and quantities. You can also mix Glossy and Matte finish in the one order, both on purpose or accidentally, so be aware of what you are selecting.