Using your G - Shock GMA - S2100P - 4A watch is a breeze. To set the time, look for the buttons on the side of the watch. Press and hold to enter the setting mode, then use the buttons to adjust the hours, minutes, and date. The countdown timer is handy for various activities. Just set the time you want to count down from and press start. The double LED light on the face and the LED backlight for the digital display can be activated by pressing the designated button when it's dark. When it comes to the mute feature, it's great for when you don't want any beeps. Simply switch it on in the settings. As for maintenance, keep it away from extreme temperatures and strong magnetic fields. If it gets dirty, you can gently wipe it with a soft, dry cloth. And don't forget, even though it's water - resistant up to 200 meters, it's not recommended to use it for deep - sea diving without proper precautions. Also, when the battery runs out after about 3 years, have it replaced by a professional to ensure it works properly.