Intro...
One of flash's easiest functions to learn is motion tweening. Yet it can be used in so many different ways, and is an invaluble tool that ensures smooth animations, and small filesizes. It also is very fast.

The Idea..
Basically a motion tween fills in steps. If you have two keyframes where an object is different or changed, it will make a gradual change inbetween the two main frames. It fills inbetween, hence 'tween'.

How?
First you need a symbol (graphic, movieclip or button). It must also be the only symbol on a single layer. You cannot tween two objects on the same layer!Now bring the symbol onto the main stage. On the main timeline, create another keyframe however far down you want. Now on that keyframe, make whatever alterations you want to the symbol. Finally, on any frame inbetween, right-click and select create motion-tween. That's it!

Different uses of tweening
Tweening can be used for many different animation techniques. In the tutorial you will find quite a few. To switch between examples, click on "scene" in flash and choose whatever section.
Basic Motion Tween: This outlines how to quickly and easily make an object move.
Alpha Tweening: This looks at how you can use tweens to make an object fade in and out. Adjust the object with the path: frame panel>effects>alpha
Scaling: This shows how you can make an object shrink and grow. Adjust the symbol throught the path: modify>transform>scale
Rotating:This shows how with the tweening properties box you can make an object rotate. Path to take: frame panel>tweening>rotate.. Note you can rotate something manually with :modify>transform>rotate if you don't want a full 360 rotation.
Scaling with Rotating: This shows how you can make an object flip and go around 360 degrees. Path to adjust objects: modify>transform>flip horizontal and frame panel>rotate>ccw or cw
Erasing and Tweening: This just shows how more interesting/realistic effects can be achieved with erasing in your tweens. Path to adjust the tween is: frame panel>erasing

Conclusion
If you don't know tweening you should. It is a must for any flash designer to know. And it's easy, and less frustrating than most other techniques. Try and complete or duplicate the 'already done' tweens in the .fla on the 'try it yourself' layer. Happy tweening:)!