A block and tackle can reduce the amount of energy (force) required to lift an object. While the device is quite simple, the rope must be properly threaded through the device in order for it to work properly. The device is very simple, as is the proper threading of the rope.
Secure pulley number one to the anchor point. (See diagram.) Be certain the anchor point can support the amount of weight to be lifted.
Thread the rope over the top of pulley number one entering from the right side, allowing it to descend toward pulley number two.
Thread the rope through pulley number two. The rope must enter pulley number two on the left side and exit on the right side.
Extend the rope upward to the base of pulley number one, which will act as the second attachment point.
Attach the object (load) you are about to lift to pulley number two. The force lifting the object will be applied to the rope extending out of pulley number one.