Camber is the angle of the tops of the wheels from straight up and down. Leaning in is Negative Camber, leaning out is Positive Camber.
As a car turns, the chassis rolls. As the car rolls, this causes the tires to lean over towards the turn, causing less tire to come in contact with the ground (at 0deg Camber). So to compensate, we add a few degrees of negative Camber. When the same car rolls, it rolls up on to the negative Cambered tire, now setting the tire at 0deg, or the largest possible contac6t patch the tire can have. As we all know, the larger the contact patch, the more the tire is in contact with the ground, and the most possible traction you can have.
Camber is usually adjusted by turnbuckles that pivot the wheel from the lower outer hinge pin. Some cars use what’s called a Pivot Ball Suspension…the steering block is attached to the A-Arm by a Pivot Ball. Screwing the upper Pivot Ball in will add Negative Camber, while unscrewing the same Pivot Ball will remove Camber, setting it closer to 0deg.