Jumping and fps

1

Hey,
I see some games where there are fps counters at the bottom, how can fps shift ? And what does it help do ?
Next, I need a jumping code, that will allow me to have one MC only as ground instead of 15 000 little ground MC’s put together and 15 000 extra code line to it.
My script so far is :


onClipEvent (enterFrame) {
	if (Key.isDown(Key.LEFT)) {
		this.gotoAndStop("walk left");
		this._parent.ground._x += 4;
		$main = "main left";
	} else if (Key.isDown(Key.RIGHT)) {
		this.gotoAndStop("walk right");
		this._parent.ground._x -=4;
		$main = "main right";
	} else {
		gotoandstop($main);
	}
}

Basically, I can make the man run and when I let go ( gotoandstop($main) ) he will stand normally again facing the direction he last was looking.
Is it possible to add a SPACE bar script to jump please ?
Oh, and could it be done :
Making the guy reach a certain speed (accelerate) and on let go, skid a bit.
thank you