Initially, you have a 33% chance to pick a car and a 66% chance to pick a goat.
When he reveals a goat, if you picked a goat door, you now would switch to the car with still a 66% chance
If it was set up with a goat in 1, a goat in 2, and a car in 3. you pick door 1 and so door two is opened and you switch to a car. if you pick door 2, door one is opened and you switch to a car. If you pick 3, either one or two is opened and switching gets you a goat. Sorry :(
If you pick the car first then you get a goat

also if I didn’t help the confused try this video:

https://www.youtube.com/watch?v=mhlc7peGlGg&t=1s