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 power reserve indicator tells you the time the watch will continue to function. It can either be seen on hand winding or automatic watches.
Watches featuring a small seconds have a smaller subcounter, usually located at 6h, which indicates seconds.