A utility patent is based on the functionality, process, and/or method of an invention and the problem it solves. Typically, a utility patent describes a problem to be solved, the history or background of the problem, other potential methods by which the problem was attempted to be solved by others, and the description of your novel (new, unique) invention and how it solves the aforementioned problem (in new ways or, taking into account previous inventions – better or different ways than existing designs).
A design patent is based on the shape or design of the device being patented. Similar to a utility patent, the design of your invention needs to be novel (new, unique). The design itself can be functional (solving a problem, providing a purpose) or non-functional (aesthetic). Design Patents refer almost exclusively to the design aspects (shape, color, organization of parts) and do not necessarily have anything to do with functional aspects of the device. As such, there is much less complexity or written protections to a Design Patent as it is not about protecting the device’s function or the solution it provides, but only how it ‘looks’.