How does the tolerance to Alcohol begin?

I guess with this question, I actually kind of have 2 questions:

1: How does the Tolerance to the burn of alcohol begin? Or, rather, how does it stop making you gag and become tolerable to throw back? I remember when I was younger I used to cough or gag when taking a shot. Nowadays, I just kinda of breathe out and it’s done

2: The body goes and processes alcohol differently when you have frequented it enough; When does that typically start and is that permanent?