Levers are the simplest form of mechanism and date back to way beyond the time of stone age man. By using a stiff branch resting on a log, early man was able to move heavy loads such as rocks. This is similar to the way we use a screwdriver to lever the lid of a paint tin.
A lever is a rigid beam that can rotate about a fixed point called the fulcrum. An effort applied to one end of the beam will cause a load to be moved at the other. By moving the fulcrum nearer to the load, you can lift a large load with only a little effort. (This is called mechanical advantage.)