Steering - sounds so obvious you may be wondering why does it deserve an entire article, other than have some more ad impressions :). Well, you steer a dirt bike in many ways, some obvious and some not... read on.
A fair definition of steering is changing direction. While motorcycles are normally steered via Countersteering, the idea is to get it leaned over and that initiates the change in direction. Dirt bikes work the same way, but... while you do have to lean them over, there are more ways to quickly change direction.
At any speed higher than walking pace, motorcycles change direction essentially by leaning over. While Countersteering gets a bike leaned over the fastest, that's not the only way. The next best way to steer a motorcycle is weighing the pegs.
Intuitively, placing more weight on the inside peg (or the one that will be the inside peg), you get the bike to lean that way. It's slower than countersteering the bars, but it can certainly help speed up the movement.
After pushing in the inside peg to get the bike to lean over, during the actual cornering, weight is shifted to the outside/higher peg, to add more stability and traction.
Another way to very quickly change the direction is to lock up the rear wheel and slide it around until the bike is pointing in the new direction. This is heavily used on dirt bikes at lower speeds and tight corners.
You can certainly try it with a road bike as well, but it is very dangerous. Asphalt offers a lot more traction than dirt, so when the wheel regains traction, there will be a big jolt that may even throw you off the bike (a High Side++).
On dirt though, the much lower traction is also a blessing from this point of view, because you can freely slide your rear tire around, without worrying about high siding the bike.
The basic mechanism of steering with the rear brakes is:
This is discussed discuss this in more detail under Brake steering.
Similarly, you can steer with the throttle, which is also applied to the rear wheel.
While you can certainly use it at lower speeds, to complement sliding, this is often used in faster, sweeping corners.
The basic mechanism is:
This will result in the rear wheel spinning faster and, by lossing some of the traction, it will complete the turn and point the bike the other way faster than just cruising around.
Note that you are supposed to use some throttle in every turn, to keep the bike planted and tracking properly. This technique involves more throttle than usual.
Here is a great visual for both brake and throttle steering:
This is a combination of all the above techniques: leaning the bike, whip it around with the rear wheel and complete the steering with the throttle and accelarating out of the turn.
See the whipping technique here:
See more cornering techniques under Cornering.