Script Refence

//Uncomment the 'elses' to prevent the object from moving diagonally.
mc.onEnterFrame = function() {
	if (Key.isDown(Key.LEFT)) {
		this._x -= 10;
	}
	//else    
	if (Key.isDown(Key.RIGHT)) {
		this._x += 10;
	}
	//else    
	if (Key.isDown(Key.UP)) {
		this._y -= 10;
	}
	//else  
	if (Key.isDown(Key.DOWN)) {
		this._y += 10;
	}
};

//Uncomment the 'elses' to prevent the object from moving diagonally.
var lstr:Object = new Object();
lstr.onKeyDown = function() {
	if (Key.isDown(Key.LEFT)) {
		mc._x -= 10;
	}
	//else     
	if (Key.isDown(Key.RIGHT)) {
		mc._x += 10;
	}
	//else     
	if (Key.isDown(Key.UP)) {
		mc._y -= 10;
	}
	//else   
	if (Key.isDown(Key.DOWN)) {
		mc._y += 10;
	}
};
Key.addListener(lstr);

if (a>b) {
//If a is bigger then b
}
if (a<b) {
//If a is smaller then b
}
if (a>=b) {
//If a is bigger or equal to b.
}
if (a<=b) {
//If a is smaller or equal to b.
}
if (a==b) {
//If a is equal to b.
}
if (a!=b) {
//If a does not equal b.
}
if (!a==b) {
/*Another way of saying the above, obviously you can replace the '==' with whatever conditions you want.*/
}

//Portable function, m is the x property of the original movieclip.
//i is just a counter that begins at 1.
duplicate = function (m, i) {
	duplicateMovieClip(ball, "ball"+i, getNextHighestDepth());
	setProperty("ball"+i, _x, m);
	if (i <= 20) {
		duplicate(m+=20, i+=1);
	}
};

mc.onEnterFrame = function() {
if (mc1.hitTest(other_mc)) {
//Do what you want when the object hits the other object.
}
}

your_mc.onEnterFrame = function() {
	if (your_mc, hitTest(your_other_mc)) {
		//put here what you want to happen if your movie clips are colliding;
	} else {
		//you can put something here if you want something to happen when the movie clips are NOT colliding;
	}
}