Using your Merida Matts 7.10 - D is a breeze. First, adjust the seat to a comfortable height. For different terrains, use the Shimano Tourney 3x7 speed drivetrain to change gears. When you need to stop, simply squeeze the hydraulic disc brake levers. Remember, always wear a helmet for safety. Before each ride, check the tire pressure and make sure the brakes are working properly. As for maintenance, clean your bike regularly, especially after riding on muddy trails. Lubricate the chain every few rides to keep it running smoothly. If you notice any issues with the frame, brakes, or drivetrain, it's best to take it to a professional bike mechanic.