What is the
out-in-out method and how is it done? The explanation is simply going around a corner at the fastest speed. There are two ways to be fast: you can either travel a smaller distance, or do it at higher speed. Or you can combine both. This means that the path your car travels should be short as well as without any sharp turns. Below will be 2 examples showing you the
out-in-out method on a 180 degrees hairpin turn and a 90 degrees turn.

This drawing shows the ideal line through a simple, 180 degree corner. The ideal line is drawn in
red, and the track edges in black. This type of driving line is called
Out-In-Out: approaching the corner, you take the outside, as far as possible, you take the inside line in the middle of the corner, and you take the outside again on the exit. The middle part of the corner, drawn in
blue, is called the apex of the turn, or the clipping point. The wider you can make the radius of the line, the faster you can take the corner. Or in other words, the less speed you'll lose.
Note that all the braking should be done in the straight line, before the circular part begins. The acceleration too begins after the circular part, when the car is tracking straight. During the circular part, the car's velocity is constant. It has to be, assuming that the radius of the path is constant and the tires are delivering maximum grip.

The same goes for any type of corner: the line with the largest radius is the fastest one. A 90° turn is pictured: brake, turn in, keep the radius of the turn constant, so don't accelerate or brake, and then straighten up and accelerate. You begin and end the corner on the very outside, and almost clip the
apex in the middle part.
The most important thing isn't to know where the ideal line is and try to stay on it, it's being able to stay on it the whole time, without any wild moments, going sideways or braking too soon or too late. Consistency is the key: never lose the momentum. You lose more time if you mess up once than you can gain rounding 10 other corners perfectly.