A crane can be broadly defined as an piece of machinery used to lift heavy loads. The most recognizable cranes are probably the tower cranes that you see on top of skyscrapers and the boom lifts used on construction projects. These two types of cranes illustrate the two basic categories of cranes: the jib and the boom.
A jib crane consists of a horizontal arm that attaches to some sort of vertical support. In the case of the skyscraper, you have a mast or tower extending up from the skyscraper and a jib extending perpendicularly from this tower. Jibs can also be used to good effect in a factory setting. You could, for example, use a wall-mounted jib to lift items from one conveyor belt to another. In this case, the jib should pivot at its connection point so that you can lift the load, rotate, and then drop the load. To increase the range of movement of a wall-mounted crane, you might have a hinge point on the jib. This hinge will facilitate picking up an object around a corner and then moving it to a new location. The final feature to look for on a jib crane is the ability to telescope. In this case, the jib comes in sections, and each section slides into the previous section so that you can easily extend the crane to cover a wider distance. If needed, you can buy used crane jibs to replace faulty sections.
In the case of a boom crane, you should have a platform to which one end of the boom is anchored with a pivot. A hydraulic lift is then used to raise the boom. The boom should also have a cable that you can use to hook objects to lift. Besides a hydraulic arm a boom lift might have telescoping sections and a hinged jib on the end. The jib should fold back against the boom and gives the crane more versatility in how it is used. Most mobile cranes feature a boom mounted to a vehicle in some way.
If you need a crane for a stationary application such as an assembly line in a manufacturing plant or an unloading station at a railway or shipyard, then you will most likely make use of a jib crane. On the other hand, if you need a crane that you transport from job site to job site, then a boom crane, will serve you best.