How to Drive
For your first driving experience you will want to try Driving School. This is a test area where you can drive (and shoot) to your heart's content. See the Driving School section in the New Player Startup guide.
For the very basics, you set your steering with the left and right arrow keys, speed with the up and down keys. You can also steer by "grabbing" the top of the wheel with your mouse.
NOTE: A disadvantage to using the mouse to move the steering wheel is that you will not see the changes to your ghost until you release the mouse. Using the keyboard provides much better visual feedback.
There is also a matter of camera perpective. For more information see the section on Keyboard Input.
The first thing you'll notice is that the game does not happen in real time. It happens in turns that represent one second of game time. This is because in a real fight you'll have many things to be doing, and possibly be managing multiple vehicles simultaneously. Thus, if you set your speed to 70mph your car accelerates each turn until you reach 70mph.
To help you, your car has a Ghost. This shows what your car might look like after your move. This ghost becomes more accurate with a higher driver skill.
Also there is a colored ring around your car. This does two things. First, it is like the ghost in that it gets larger the faster you are going. Second, the color is an indication of the stress level of the characters in the car. Green is fine, Yellow is stressed, and Red indicates panic. (Blue is shown when you can see a vehicle's speed but have no way of knowing the stress level of the occupants.)
Driving is not as straightforward as one might think. New players have a tendency to "drive off their ghost" and simply point it where they want, but if you watch your car as it moves you will see that it might be turning normally or perhaps it might be about to slide out, for instance. The interface may seem simple but the physics are there. Cars will swerve, fishtail, drift, etc. The car may be pointed in one direction but may be traveling in another.
One good way of learning how cars handle is to practice with races, that way you can concentrate on your car's movement with no distracting weapons fire, as cars are also affected by recoil from being hit by, and even by firing, weapons.
Hint: You can even zoom in real close and see how the tires are affected by small fluctuations in the terrain. Terrain can look different from different angles.