Team Fortress 2, or TF2 is a FPS - First Person Shooter. There are 9 different classes, organised into 3 different categories. Offense - Scout, Soldier, Pyro. Defense - Demoman, Heavy, Engineer. Support - Sniper, Medic, Spy These definitely aren't definitive though.
Scout is the fastest class, he can double-jump, and with the right combination of weapons he can even quadruple-jump! (with the Atomizer and the Force-A-Nature). He is best at hi-and-run attacks, and is especially effective against Snipers, as Scout is so fast.
In my opinion, the best Scout weapon by far if the Force-A-Nature, it sends people flying backwards! This makes it good against Heavies. If you do a triple-jump with the Atomizer and then fire the Force-A-Nature at the ground you can quadruple-jump!
I'm running circles around ya!
Soldier is, according to Valve (who made the game) the easiest class the learn. He can do a Rocket-Jump which sends him pretty high up in the air, and you can also get the Rocket Jumper, which doesn't do anyone any damage, so is useless in a fight.
Pyro is quite fun, as you can kill people after you've died, if you set them on fire. The pyrovision goggles can be equipped by any class, and there are a few items that enable pyrovision when equipped. It is always best to approach enemies from behind, especially with the Backburner. Also, you can put out fires on team mates by using your compression blast on them (MOUSE2). This can also deflect enemy projectiles. If there is a Sniper with the huntsman equipped on your team, you can set the arrows on fire. Demoman is fairly difficult to get used to, you really need to have the Scottish Resistance equipped to be most effective, as it allows you to detonate particular groups of stickybombs at a time, and from a distance, and you can see them through walls, which can be good for ctf. You can also stickybomb-jump, though you have to be careful, as it is very easy to do too many stickybombs, and kill yourself. Heavy is the toughest class, but also the slowest. he is often best paired with a Medic. A good team has 2-3 Heavies on it. Engineer is one of my favorite classes, it is easiest to deploy in a defensive position, but you don't have to. If you try lots of places (having fully leveled up your buildings) you should be able to find a really good spot. The Wrangler is good for long-range shooting, but the big problem with it is that you cannot replenish the ammo for your Sentry, and you can get low pretty quick. Another good gun is the Rescue Ranger, which allows you to pick up buildings from a distance, thereby allowing you to move your buildings around quickly. It does use up lots of metal though.
Sniper is my favorite class, despite the fact that you are a prime target for Spies. But with the Razorback equipped, you are well defended. Find a good spot, hunker down, and shoot people in the head. That's the basic strategy. The Huntsman is good for mid-range to short-range but not long-range. The Machina is good, provided you are a good distance away from targets, because you cannot shoot unscoped. It makes you easier to find too, as it shoots tracers, though that won't be a problem as long as you don't miss. Medic is not essential, but very helpful. Especially on MvM (Mann vs Machine) as you can revive people (and then they like you) you can also do a 'Shield thingy' that absorbs damage (see new MvM trailer). On PvP, Medics are best paired with one if the tougher classes, e.g. Heavy, Soldier, Pyro, Demo. Spy is the class I'm worst at. You are the nemesis of all Snipers and Engineers, remember that you lose your disguise when you attack (even if you miss). But you don't lose it when you put a sapper on an enemy building.