How a Mechanical Watch Works
A mechanical watch is a watch that uses a mechanical mechanism to measure the passage of time, as opposed to modern quartz watches which function electronically. It is driven by a spring (called a mainspring) which must be wound periodically. Its force is transmitted through a series of gears to power the balance wheel, a weighted wheel which oscillates back and forth at a constant rate. A device called an escapement releases the watch's wheels to move forward a small amount with each swing of the balance wheel, moving the watch's hands forward at a constant rate. This makes the 'ticking' sound characteristic of all mechanical watches. Mechanical watches evolved in Europe in the 17th century from spring powered clocks, which appeared in the 15th century.
Mechanical watches are not as accurate as modern quartz watches and are generally more expensive. They are now worn more for their aesthetic attributes, as a piece of jewellery and as a statement of one's personal style, than for their timekeeping ability.
See more about mechanical watch in this video.