Caster
The fore-aft tilt of the steering axis. More positive caster gives self-centring, steering feel, and camber gain as you steer.
Caster is the angle of the steering axis viewed from the side of the car. Positive caster means the top of the axis leans backwards, which is what gives a car self-centring steering and straight-line stability.
For drift it does something more useful than either of those: it adds camber as you steer. The more lock you wind on, the more negative camber the outside front wheel gains - which keeps that tire's contact patch flatter under load exactly when the car needs it most. That is why drift setups generally want a lot of caster, and why adjustable caster is one of the markers of a real angle kit.
What you feel
More caster gives heavier steering, stronger self-centring and better feel for what the front tires are doing. On a car with no power assistance that weight is a real consideration. It also makes the car want to straighten itself out of a drift, which is helpful when you are learning and something to tune around when you are not.
Too little caster and the car feels vague and does not want to come back; it also loses the camber gain that makes the outside front tire work at high lock.
Where it comes from
Some is designed into the chassis. More is added by an angle kit or by caster-adjustable control arms and offset bushings. Published guidance on quality angle kits names Ackermann, caster and toe adjustability together, because those three are what let you set the car up rather than just steer it further.
In the build
Phase 2, and it is set at the alignment - which is why the alignment comes after the kit, the coilovers and the roll centre correction. Caster is also one of the numbers you will come back and change after your first event, so budget for a second alignment.
Questions
How much caster should I run?
Start from your angle kit manufacturer’s recommendation. More gives better camber gain and feel at the cost of steering weight, and the useful amount depends on whether you have power steering and what your tires are doing.
Does caster make steering heavy?
Yes, and noticeably so on a car without power assistance. It is one reason a smaller-diameter steering wheel and a healthy rack matter on a high-caster setup.