Using your Longines 40mm Master Collection Moonphase watch is easy. Just wear it on your wrist like any other watch. The hands show the hours, minutes, and seconds clearly. The small hand at 6 o'clock indicates the date. You can also admire the beautiful moon phase display on the dial. As for water resistance, it can handle splashes and short periods in water, but don't take it for a long swim or diving as it's only water - resistant to 3 bar. To keep it in good condition, clean it regularly with a soft, dry cloth. Avoid hitting it against hard objects as it may damage the case or the internal mechanism. Also, make sure to wind the automatic movement by gently shaking the watch or wearing it regularly to keep it running smoothly.