A lever is a simple machine that consists of a rigid bar that pivots around a fixed point called the fulcrum. The fulcrum divides the lever into two arms: the effort arm and the load arm. The effort arm is the part of the lever that the force is applied to. The load arm is the part of the lever that the load is applied to.
The mechanical advantage of a lever is the ratio of the output force to the input force. The output force is the force that is applied to the load arm. The input force is the force that is applied to the effort arm.
The mechanical advantage of a lever can be increased by increasing the length of the effort arm or by decreasing the length of the load arm.
The direction of the force is also changed by a lever. The input force is applied in the direction of the fulcrum, and the output force is applied in the opposite direction of the fulcrum.