There are two reasons why you would have white edges on your prints - Borders, and Letterboxing.
If you have a white edge of approximately equal thickness on all four sides of your print, this is called a border. This is one of the options you can choose when you are adjusting the settings for your image as shown below. If you don't want borders, just leave this option set to NO BORDER (the default). The only way borders will be applied to your images is if you add them yourself.
If you have edges of roughly equal thickness on two sides of your print, this is called letterboxing. During the Review Crop step of the print wizard, you will be provided with the option of letterboxing your images by clicking a check box (See below)
if you choose to letterbox your images, the full un-cropped image will be centered on your print, and if your image isn't exactly the same proportions as the print size you chose, any excess space will be left as white borders to either side, or above and below your print (As shown below).