The six simple machines are the inclined plane, wedge, screw, lever, wheel and axle, and pulley. Each machine is capable of reducing the amount of force needed to complete a task.
The inclined plane is used to move objects from a low position to a higher position without having to lift them. Lifting requires more work than pushing up an inclined plane.
A wedge is used to open something or push things apart. The narrow edge fits into a small space. When the wider edge is struck, the wedge slides into the space, creating a wider space.
A screw allows one object to be forced through another. It is often used to hold objects together. A lever is used to pull small objects loose from larger objects by using an arm and fulcrum to give additional force.
The wheel and axle reduce the amount of force necessary to move objects over long distances. A pulley lifts, lowers and moves objects without the need for much additional outside force.
To further reduce the amount of force needed to complete a task, simple machines can be combined to form compound machines. A compound machine can be made of two or more simple machines working together.