Using your G-Shock GA100RC-1 men's watch is a breeze. To set the time, use the buttons on the side of the watch. Press the mode button to switch between different functions like the world time, stopwatch, and countdown timer. To set an alarm, find the alarm - setting mode and use the adjustment buttons to set the time and choose which days you want the alarm to go off. When using the LED light, just press the designated button for a bright illumination. For the stopwatch and countdown timer, start and stop them with the appropriate buttons. As for maintenance, keep your watch away from extreme heat or cold. If it gets wet, dry it with a soft cloth. The battery usually lasts about 5 years, but when it starts to run out, take it to a professional to replace the CR2016 battery. And remember, since it's water - resistant up to 200 meters, you can wear it while swimming or doing water - related activities, but avoid pressing buttons underwater.