Road racing comes down to cornering in the end. The driver who is able to sustain the highest speeds through the turns will have the lowest lap times, assuming the cars to be of equal configuration.

Braking and accelerating into and out of a typical corner. Note the pedal pressure variation during the course of cornering.
To get familiar with the terminology first, every corner is made of three parts. They can be termed as the entry, the apex and the exit.
The entry is the point at which a turning begins. The apex can be defined as the point where the car reaches the furthest point on the inside of the turn. It is at the exit where the car completes the turn and start to drive straight. While driving through a corner or a series of corners, the main objective is to have the maximum possible speed at the exit of corner, or at the last corner of a series. It is not necessary to have the maximum speed
The objective in driving through a corner, or a series of corners, is to have the fastest possible speed at the exit of corner, or the last corner of a series. It is not necessarily to have the fastest speed going into the corner, nor even the fastest speed in the middle of the corner. The last corner exit before a straight is the most important segment. The speed of the exit determines the speed during and at the end of the straight. If you can increase the average speed of an entire straight, that will have greater impact that a faster average over the shorter distance of the entry to the turn, or through the turn itself. The path, or “line” you drive through a corner will determine the exit speed. In general, the fastest line through a corner is the one that allows the greatest radius, or straightest path. As a car can go faster around a large corner than it can around a tight corner, the shortest path around a corner is rarely the fastest. To illustrate these concepts so far, the classic teaching aid is to look at a 90-degree bend. In the illustration below, the dotted line follows the path of the road. The solid line indicates a path that maximizes the radius of the turn, or attempts to make the turn as straight as possible. As you can see there is significant difference in the tightness of the turn that follows even the outside of the road compared to the one that utilizes the whole width of the road surface.

Cornering
As mentioned, the objective in any corner is to have the highest exit speed. Taking a line that allows the earliest possible point to get back into the throttle is also involved apart from increasing the corner radius. In order to do this, the car should straighten back out on the corner exit path at the earliest. The above corner line can be modified further to allow this. In the image below, the previously mentioned large radius path is illustrated by the dotted line. The solid colored line indicates a path known as the “late apex”. This path moves forward to the point at which the car reaches the corner apex. The exit path of the car gets straightened by the late apex, and therefore allows the driver to accelerate earlier. This helps to increase the exit speed, and it in effect helps to lengthen the straight, that allows to achieve higher speed at the end of the straight.

Ideal Line
There is still a faster technique for most of the corners, while the geometric racing line is faster than the natural line of the road. The theory behind the technique is using the late apex. The car can aim to apex later than the geometric apex point, by delaying the turn in point, and beginning the turn with a slightly sharper bend. This helps to straighten out the second part of the turn, and thus allows the driver to throttle early. Even though the car will have to slow down more at the turn in phase, the exit speed will be higher. This exit speed helps the driver to achieve that much more speed on the straight, which will bring down the overall lap times.