It is the button on the end of the spindle that is used for adjusting the time and/or date on an analogue (non digital) watch. In older watches and pocket watches which are not powered by batteries it is also used to wind the watch spring to give it power. Generally the winding is done with the crown flush against the watch, pulled out once it adjusts the date (if it has one) and pulled out a second "click" it adjusts the time. The crown is generally round and ridged to provide grip on the finger.
To change the watch crown, the back of the watch must be taken off. The inner workings of the watch are then removed, and the old crown taken out. The process is reversed to put the watch back together. Some of the fancier watches have a crown that can be unscrewed from the outside.
A crown stopper is a feature found on some watches that prevents the crown from being pulled out inadvertently, thus protecting the watch from water damage. It can be a screw-down crown or a push-in crown with a locking mechanism to secure it in place.
crown: Also called a stem or pin, a crown is the knob/button on the outside of the watch case that is used to set the time and date. In a mechanical watch the crown also winds the mainspring. In this case it is also called a "winding stem". A screw in (or screw down) crown is used to make a watch more water resistant. The crown actually screws into the case, dramatically increasing the water-tightness of the watch.
To set an Activa watch, first pull the crown (the small knob on the side) out to the second position to set the time. Rotate the crown to adjust the hour and minute hands to the desired time. If your watch has a date function, pull the crown to the first position and rotate it to change the date. Finally, push the crown back in to start the watch.
Rolex
I own an AT0875-09E, and can report that the crown does not screw down, although the watch is WR200. I have swum with it with no problems.
To set the time on your TechnoMarine watch, first locate the watch crown on the side of the watch. Pull the crown out to the appropriate position (usually position 2 for time setting) and then turn the crown to adjust the hour and minute hands to the correct time. Once you have set the time, push the crown back in to secure the settings.
To set the time on a Charles Raymond watch, locate the crown on the side of the watch. Pull the crown out to its second position and rotate it to adjust the time. Once the correct time is set, push the crown back in to its original position.
To set a multifunction relic watch, first, locate the crown, usually on the side of the watch. Pull the crown out to the first or second position, depending on whether you're setting the time or date. Rotate the crown to adjust the hands or date, then push the crown back in to finalize the settings. Always ensure to consult the specific manual for your watch model for accurate instructions.
To set a Leeda watch, first, locate the crown on the side of the watch. Pull the crown out to the first or second position, depending on whether you're setting the time or date. Turn the crown to adjust the time or date as needed, then push the crown back in to secure your settings. Finally, ensure the watch is wound if it's a mechanical model, or check the battery if it's quartz.
To change the time on a Timex Expedition watch, first, locate the crown on the side of the watch. Pull the crown out to the second click to enter time-setting mode. Turn the crown to adjust the hour and minute hands to the correct time, ensuring you set AM or PM appropriately if your watch displays it. Once set, push the crown back in to save the changes.
To wind an Ik Colouring watch, simply locate the crown on the side of the watch. Gently pull the crown out to the first position, then turn it clockwise until you feel resistance, which indicates that the watch is fully wound. If the watch has a specific time-setting mechanism, ensure that you adjust the time after winding. Finally, push the crown back in to its original position to start the watch.