Winding stores mechanical energy in the mainspring.
In former times watches (e.g. pocket watches in the beginning) were wound using a key. The key turned the square end of the spring core shaft of the barrel around which the mainspring is coiled. See also auger shaft, worm shaft
Invented in 1842 by Jean-Adrien Philippe, crown winding allows one to use the crown of the watch to turn the barrel and wind the mainspring. This method is also known as self winding, keyless winding, or hand winding.
Charles Antoine Jaeger-LeCoultre is also named as originator of the crown winding. In 1847 he invented a crown winding with a rocker, which allowed both winding and adjusting the hands using a single crown. Today, the LeCoultre method is typically used for all watches. The switching mechanism functions via pulling out the crown to the required position, in which one of the desired functions can be performed. Watches may include one, two, or even more crown positions for various functions, including winding, setting the main time or second time zone, and setting the day and date.
Many modern watches include an automatic winding mechanism. Here, the winding of the movement happens automatically by the movements of the wearer's wrist, which sets a rotating weight segment (rotor) in motion. (For details see Automatic winding.)
Note that many automatic movements may also be hand-wound. There is some debate as to whether this can damage the keyless works mechanism and clutches, however, and should be avoided with certain movements, including the popular ETA 2824-2.