How come everytime I turn my key to start the car gas pours from underneath it

Depends on where and whats leaking unfornatly I cant see whats leaking. Is it a fuel line running down from the top of the fuel tank?

Seems a pressurised fuel line, hose or joint is leaking and it can only get worse.

You would need to get under the vehicle to check where the leak is coming from and continue from there.

This is a safety hazard so you should get it done immediately and avoid starting the vehicle if possible.