What is that metal button behind the accelerator? I stepped all the way down on it while driving on the free way and i then hear a click...then my engine starts reving like crazy. What does that thing do?

aka kick down switch.

a little more detail would help me. How does that make the car go faster?

It's directly connected to the "high speed bumper bolts"

The kickdown switch is used by the transmission control unit as it manages shifting.
Hit the throttle hard & fast, to the point of engaging the kickdown switch, and you'll get a down shift more quickly than if you hit the throttle hard & fast but let up before you hit the kickdown switch.

That damn button always pisses me off when I'm trying to accellerate at high speed- it does nothing at that point .

Newbie,

At that point you need a Kleemann supercharger.

Haha, I always wish it was a Nitrous switch .