For instance, only Mattel can profit off of the official Barbie Doll, because they have the patent for that product. A general invention, machine, process, whatever. Design patents protect certain designs in manufacturing or building, based on the unique appearance of the item. If you want to patent your new breed of petunia, go find a plant lawyer. Mechanical devices composed of parts that work together to do something.
Machines can be completely new or made up with existing inventions to achieve a new purpose.
Compositions of Matter. Mixtures of stuff that have cool properties. These include drugs, chemicals or metallic alloys. Basically, a process is a way to do something. Anything that you can make that isn't a machine or a composition of matter.