Tweening is a huge time saver over frame by frame drawn animation. You set beginning and end points for your animation and Flash will draw the frames in between for you. The two types of tweening in Flash are motion and shape tweening.

Shape tweening is used to morph only very simple shapes, like a circle into a square. Shape tweens only work on shapes, not symbols or groups. Shape hinting is used to give your more control over how your shapes are morphing if you are not getting the desired results. Shape tweening in general is not as commonly used or as easy to get desired results with as Motion tweening. Note the letter transforming in an undesirable fashion.
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Motion tweening is used for moving, rotating, scaling, skewing, changing color, and transparency of a symbol, group, or editable text (shape tweening can also change color and transparency).
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With motion tweening, you put only one item on one layer to tween at a time. You use multiple layers to tween multiple items. AGAIN, ONE OBJECT ON ONE LAYER AT A TIME ONLY!

Easing in and Easing Out
You can set the easing to change the speed of your animation at the beginning or end of the tween. For example, if you need to zoom into something starting slowly and then moving in quickly as you get closer.

download the tween tutorial (file name: 3Tweentut.fla)
right click on the file (control-click for Mac) and select to download to your drive.