Don't worry, I can help you!
Before anything else, release the accelerator. This will help the car not gain any more speed, and the weight of the car should let it coast and eventually come to a stop. But before you stop, there's some important things that have to be taken into account before you act.
Firstly, judge your surroundings. Are you on an open highway? If so, just avoid any potential traffic and you should be perfectly fine. Just be early with your steering as it may not work as well as at lower speeds.
If not , then see if you can get off the road and it's a relatively uneven terrain (not too flat but not super bumpy) then try to get there. The bumps and dirt terrain should slow your car down faster than coasting on the roads.
If all else fails, you have three options:
- If you have an anchor, drop it.
- If not, try the handbrake.
- If you have neither an anchor or a functioning handbrake, well... Jesus take the wheel.
Hope that helped! :D

HELP IM GOING 200MPH AND I DONT KNOW HOW TO BRAKE PLEASE POST GUIDE!!!

simple, if you want to turn use brakes to slowdown low speed will give you cojntrol vehicle better.. ( sorry bad english )

and how fast is it in km/hr i dont speak burger per stone

Use the big wheel and turn it in the direction you wanna go.

Unless you're driving a Bugatti.

Then, as it says above, start praying or drop your anchor.

i still don't know how to turn :/

glad to hear that

HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH, the bugatti one made me cry to die

i did tried, didn't worked.

LOL