A machine is something made by humans to help with work and make life easier. There are two types of machines: simple and complex. The six simple machines are the lever, inclined plane, wheel and axle, screw, wedge, and pulley. A screw has a flat head with a spiral winding from the pointed end to the wide end. Screws are used for putting things together, as seen in door hinges, desks, chairs, basketball hoops, and fans.