Flash Pro CS4 added a whole new way of creating and editing tweened animation. Tweens are animation where you set values for different properties of an object at certain points in time and let Flash fill in the values in between.
The motion tween model is much easier to work with than older classic tweens that you had to create in earlier versions of Flash. You can literally start animating objects on the stage in just a few clicks.
If you are new to Flash Pro and want to use it for animation, here are a couple of solid tutorials that will help you learn the basics and start experimenting with your own artwork: