What is wrong with the car if u step on the gas pedal and it shuts off the car

Check throttle body and fuel pressure.

How do I check fuel pressure

With a fuel pressure gauge, if you don't want to buy one you can rent (or even borrow) one from most auto parts shops. You can google a "how-to" on using it. You may want to replace the fuel filter first if it has been a while and see if problem goes away. Problem may also be vacuum related, something like an EGR valve stuck open can cause a car to stumble when pressing gas.

Take it to a mechanic, if you have to ask how to check the fuel pressure you really have no business attempting it. No offense intended, but lack of knowledge can sometimes get us into trouble. Been there, done that.