It was really easy to do, actually. You register for a free account, and then start uploading your resized pictures (make sure they are web-ready--not larger than 800 pixels wide), and add descriptions and tags.
Be careful that you add your items to the appropriate categories--when I uploaded my first batch of items, I didn't notice there were separate categories for clothing and dolls. (The pages are actually very specifically sorted--by company/doll manufacturer, doll size, and item type.) Your first uploads and photos have to be approved--mine were within a few hours (since I posted mine in the middle of the night). And voila! There they are!