There are quite a few resources on this (when you search for "as3 use embed tag"). Some of them are really helpful: http://www.bit-101.com/blog/?p=853 http://help.adobe.com/en_US/flex/using/WS2db454920e96a9e51e63e3d11c0bf680e1-7ffe.html
The most basic thing is that you declare a variable of some type. And you use the [Embed]
tag before the variable declaration. It's some kind of weird association. Something like:
[Embed(source="image.jpg")]
public var imageClass:Bitmap;
// later on you can instantiate it and use:
addChild(new imageClass()); // creates and adds new image
This is just a sample - there are a lot of types and ways to do it - give a shot the Adobe reference, there are tons of samples.