Helical Compression Springs are the most common metal spring configuration. Generally, these coil springs are either placed over a rod or fitted inside a hole. When you put a load on a compression coil spring, making it shorter, it pushes back against the load and tries to get back to its original length. Compression springs offer resistance to linear compressing forces (push), and are in fact one of the most efficient energy storage devices available.
Helical compression springs basically are mechanical devices which store and release energy. They are used in a wide variety of applications where predictable flexibility is desired.