Using the Merida Big Seven 20 is a breeze. Just hop on, adjust the seat to your comfort, and start pedaling. When riding, shift gears according to the terrain - use lower gears for uphill and higher gears for flat or downhill sections. For braking, squeeze the brake levers gently for normal stops and a bit harder for quick stops. As for maintenance, regularly check the tire pressure. Keep the tires inflated to the recommended level for a smooth and efficient ride. Clean the bike after every muddy or wet ride to prevent dirt and grime from building up. Also, lubricate the chain every few rides to keep it running smoothly. Remember to have the bike serviced by a professional at least once a year to ensure all parts are in good working condition. And always wear appropriate safety gear like a helmet when riding.