Mountain bikes come equipped with a variety of gearing to allow riders to tackle even the toughest terrain. If it's been a while since you've been on a geared bike, or you've only ridden singlespeeds in the past, knowing when -- and how -- to change gears can be a little bewildering at first. Read up on how mountain bike gears work so you'll be ready to hit the trails.
Start pedaling your bike until you reach a steady, comfortable cadence. When you're riding a flat, the chain should be on the large chainring, by your front derailleur. The shifter on the right side of the handlebar will control the front ring, while the shifter on the left side will control the rear ring, or the cassette. Always pedal while shifting gears.
Click your front shifter to move into your middle gear, which will switch the chain to the middle chainring. This gear is used for slight climbs, when pedaling against moderate winds, or when traversing soft ground.
Keep your front gear in the lowest gear and practice shifting your rear gear up and down. Each click of your shifter should move the chain one ring on your cassette. As you shift your rear gear down, the resistance will get lighter. As you shift up to the larger cassette rings, you'll feel increasing resistance.
Shift your rear cassette to a middle gear and then click your right shifter to switch your front gear to the largest chainring. This is higher gearing, useful for riding flats or descending hills.
Gear down as you approach climbs. Waiting until you're on a climb to switch gears creates a lot of torque on the chain, is tough on the derailleurs and can cause the chain to fall off.
Practice riding a variety of terrain and switching through your gears. With time, you won't have to think about when or how to switch gears because it will become second nature.