Distribution Buildings are used to sell the products you make on the production screen. They can not sell products until they have been produced by your production facilities. Keep in mind that Production buildings don't exactly match Distribution buildings in speed on a 1 to 1 basis. Some distributors can sell product much faster than its made, and some production can make a product much faster than its distributed. This means you'll have to find the right balance of production and distribution facilities to maximize profits.