Electronic Stability Program (ESP), also called Vehicle Dynamics Control, Dynamic Stability Control, etc., is a
passive safety feature for your car that constantly verifies whether your vehicle is headed in the direction the steering wheel is indicating. If the system detects that your car is veering off the desired course, it will
instantly react by individually applying the brakes on up to two specific wheels in order to cause the car to swing back on course.
The detection portion of the system works by comparing data from a sensor embeded in the steering wheel and directional data obtained from a yaw sensor.
This type of course correction cannot be performed manually with today's cars because there is only one brake
pedal that applies the brakes on all four wheels. To manually achieve the same effect as ESP, you would need to have 4 brake pedals, one for each wheel. And you would need to instinctively know which brake pedal would have which effect under any given circumstance, such as oversteer or understeer.
The ESP system can apply the brakes to the wheels of its choice thanks to your car's ABS system which is already designed to be able to individually control each wheel's braking.
To visualize how the system uses the brakes to correct your car's course, suppose that you are traveling straight and you hit "the brake for the left rear wheel". This will cause your car to tend towards rotating left. Simulate it with the help of a pointy knife and a piece of paper that represents a car. Move the piece of paper forward on your table and while you are doing so jab the knife in the area of the paper where the left rear wheel would be. Notice that your forward pushing of the paper now causes it to rotate left instead of move forward. The knife, of course, represents the friction of the wheel being braked (Note: this excercise will probably damage your table). In a real world situation, suppose you wanted to turn left but the car started to skid straight ahead. Hitting the left rear wheel brake pedal might allow your car to regain its full grip on the road and thus go where you want it to.