You may or may not be aware of the different branches of Mountain Biking which have become popular over the last 5 or 10 years, so I'll give you a quick intro here on what each of the best known are about.
Cross Country, or just XC: this is more or less what you can see in the photo above - you get out in the countryside, off the roads, or at least main roads, and ride! Hardtails and 3 to 5 inches of suspension. Serious athletes compete at the top end, people like us troll along at the other extreme.
Downhll, or DH: Big, burly full suspension bikes with 6 to 10 inches of suspension travel front and rear and you simply throw them off the top of a hill and pray! Quickest woman or man down to the finish line wins, against the clock. Normally very rough, dangerous courses for extreme riders only.
Freeride: A vague mix of everything, usually with 6 inch travel bikes or more, doing a bit of everything, either seriously or just for fun. Bikes a bit heavy to drag up mountain sides.
Dirt Jump: This is for the Upside Down Brigade who usually lay out a short series of ramps and jumps a few hundred metres long and see who can touch the least ground on the way to the end. Hardtail originally but more recently full suspension bikes are being used.
Four Cross, or 4X: This is the Mountain Bike version of BMX on a short track with banked turns ("berms"), jumps and "tabletops" where four riders race each other from a standing start and the survivor normally wins. Short travel full suspension or hardtail bikes are used.
Dual or Duel: Four Cross with only two riders!
Trials: The pushbike version of motorcycle trials, but with even more skill than the amazing motorbike riders need. Almost solely using hardtail bikes.
