Worldtime watches indicate on their dial the most important cities of the 24 different time zones worldwide. You can simultaneously tell the time of all these cities.
Watches featuring a GMT complication (which stands for Greenwich Mean Time) can display a second time zone thanks to an additional hand. They are much appreciated by travelers and airline pilots.
The date is a small window on the dial which indicates the day of the month (between 1 and 31).
The central second is the central hand of the dial which divides the minute into 60 units.