Create four Buttons on your stage.
Give the first an instance name of bSlow.
Give the second an instance name of bStart.
Give the third an instance name of bStop.
Give the last an instance name of bFast.

Create a MovieClip of a happy face on the stage.
Give it an instance name of mcFace.

Actionscript:

//variable to hold the speed
var speed:Number=.1;

bSlow.addEventListener(MouseEvent.CLICK, fSlow);
bStop.addEventListener(MouseEvent.CLICK, fStop);
bStart.addEventListener(MouseEvent.CLICK, fStart);
bFast.addEventListener(MouseEvent.CLICK, fFast);

function fSlow(event:MouseEvent):void {
speed=speed-1;
mcFace.rotation+=speed;
}

function fStop(event:MouseEvent):void {
speed=0;
mcFace.rotation+=speed;
}

function fStart(event:MouseEvent):void {
addEventListener(Event.ENTER_FRAME, fSpin);
speed=1;
mcFace.rotation+=speed;
}

function fFast(event:Event):void {
speed=speed+1;
mcFace.rotation+=speed;

}

function fSpin(event:Event):void {
mcFace.rotation+=speed;
}

Example:

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