The crane may look like it's a really complex machine with all the various parts and pieces to it. But, it really isn't that complex when it comes down to the basics. At its most basic, a crane is a series of simple machines.
A simple machine is a force multiplier. It takes the force that you put into it and then makes it stronger. Think of a pulley. When a pulley is set up correctly, you can put a little bit of force behind the rope or other device and then the pulley takes that force and increases it. That will let you pick up a heavier weight than you could pick up on your own. There are traditionally six simple machines, the pulley, the lever, the wheel and axle, the inclined plane, the screw, and the wedge. Each of these simple machines takes the force that is put into it and multiplies and/or redirects it. In a crane, there are three simple machines that you are going to see, the lever, the pulley, and the wheel and axle.
A lever is a beam or some other kind of rigid rod that is balanced on a fulcrum. The fulcrum is the point on which the lever moves. Think of a seesaw. The parts where the kids sit are the lever, the beam that runs under that part, in the center, is the fulcrum. The children sitting on either end are able to exert a little bit of force and lift the child on the other side up. Some seesaws will let someone adjust the position of the seesaw a little bit to change where the fulcrum hits, allowing for a lighter child on one end to lift up a child that is heavier than they are.
The pulley is basically a wheel with a groove for a rope or cable to run through. When you pull on the rope on one side, it lifts a heavier weight on the other end. You can use a series of pulleys in concert to lift even heavier loads. An example of this is the compound bow. There are a series of pulleys on the bow that will allow you to use less force to pull the full weight of the bow.
A crane may look complex, but in reality, it's just a series of simple machines that use physics to lift up very heavy loads. Contact a company like PMM Cranes for more information and assistance.