This article gives general information about design patents
A design patent allows you to protect the "ornamental design of a functional item" for 15 years. By protecting an item's look, form, and structure with a design patent, you prevent others from manufacturing or importing that design unless you sell or license those patent rights.
A few examples of design patent categories include jewelry, clothing, furniture, a beverage container, or even a computer icon.
In contrast with a utility patent, a design patent does not protect an item's function. If you created a modern-looking chair, you invented that modern look, not the chair itself.
Design patents are intended to protect the unique look of a functional item. For example, Oakley uses a design patent to protect the different form and shape of their unique sunglasses (see their patent below). However, the Oakley symbol or any decals put onto the sunglasses would not affect the physical design of the actual item itself. Symbols or decals would be protected by trademarks as opposed to patents. Furthermore, paintings do not apply to a functional item and are protected by copyrights. Finally, a unique pattern or illustration put onto a shirt would be protected by copyrights as well. However, if the shirt had a unique collar or a strange-looking sleeve, it might qualify for a design patent. Naturally, it is often confusing as to what form of protection a new idea or invention may require. A professional will be able to help you determine how to best develop your idea.
A famous design patent is Coca-Cola's unique bottle shape. See their original patent below along with a few other design patents. You may realize that you have potential design patents stored in your head this whole time.