>What does Adderall do from the perspective of the person taking it?

It makes tasks feel more rewarding.

>Do their thoughts stop racing?

Not directly, but rather than go back and forth between different trains of thought, it's easier to stick to a single one which is a lot less stressful.

>Do their thoughts still race, but they can be traced for longer?

I feel that racing thoughts are a product of not thinking them to their conclusion. Once concluded, they can be let go easier.

>Do they have the ability to lock onto, and stick with a particular thought rather than their focus drifting all the time?

Yes. It's easy to stay focused on something that feels rewarding and meaningful. Adderall lowers the bar for "rewarding enough" to stick with something.

>What happens when you take Adderall for a few months?

The effects diminish a bit, especially the euphoria which is common in the beginning, but it remains quite effective nonetheless.