The mainspring: stored energy
Winding a mechanical watch tightens a coiled mainspring inside the barrel. As the spring unwinds, it turns the barrel and supplies torque to the movement. A manual-wind watch is wound through its crown; an automatic watch also has a weighted rotor that winds the spring as the watch moves on the wrist.
The movement's power reserve is the approximate time it can run after being fully wound, under the conditions defined by its maker. It is not a measure of accuracy, and real-world running time can vary with usage and complications.
The gear train and hands
A sequence of wheels and pinions transfers energy from the barrel toward the escapement. Their gear ratios translate the barrel's rotation into the speeds needed for the seconds, minutes and hours displays. The familiar one-revolution-per-minute seconds hand is only one display arrangement; some watches use a small seconds subdial or no seconds display at all.
The motion works and hand-setting mechanism connect the crown to the display. A date or other complication adds mechanisms that perform functions beyond basic hours and minutes, often drawing more energy and increasing mechanical complexity.
The escapement and oscillator
The escapement releases the gear train's energy in small, regular increments. In a traditional wristwatch, the balance wheel and hairspring oscillate back and forth; the escapement interacts with that oscillator to govern the rate at which the hands advance. The sound often described as a tick is this repeated action, though many high-frequency movements sound more like a rapid buzz.
Lubricants, materials, geometry, temperature and position all influence performance. A mechanical watch is a precision instrument, but it remains sensitive to shocks, magnetism, wear and how it is worn. Manufacturer guidance is the best reference for winding, storage and care.
Manual wind versus automatic
A manual-wind movement asks the owner to wind it regularly and often permits a slimmer case because it has no winding rotor. An automatic movement can keep its mainspring wound during normal wrist activity, but it still stops when its reserve runs down and may require winding or setting after time off the wrist.
Both are mechanical watches and can share similar architecture. The practical difference is how energy reaches the mainspring, not whether one is truly mechanical and the other is not.