Welcome...
Start by owning a car capable of it, its allot easier / usually cheaper to buy one that is already setup... Additionally it is usually less hassles if your drift car isn't registered and you trailor it to / from the track. What do you own now?
Then register for private track days and show up and drive. There are a few clubs which run them and we will be looking at running them soon too. When you start getting better you can enter comps and that.
Another recommendation is that "if you can't afford to set the car on fire and walk away from it, then you can't afford to be racing / drifting it"