Tweening is short for 'In-betweening'. Tradtional cel animation is very time and labor intensive, so the practice developed where the lead animator would draw the 'key frames' (the frames where the action starts and ends) and an 'in-betweener' would draw the actions between the key frames (in-betweening).

Flash does away with the job of the in-betweener. In these series of tutorials you will experiment with both shape tweening (having an object change from one shape to another) and motion tweening (having an object move from one place to another).

Let's do a simple shape tween

Step 3 - Click on a frame inbetween your two keyframes. And in Properties select Tween - Shape

Under Control Play your movie.

See how the oval changes shape to a rectangle?

Step 1 - On the Stage write the words: frog movie. You can use any font. I used Comic Sans

Insert a Keyframe and another Keyframe about 35 frames in.

Add a new layer and add the words My on the second layer

Step 2 - Flash will not let you shape tween text unless you break it apart.

With the Arrow tool select the word My and under
Modify > Break Apart break apart the text. It now becomes a shape and can be shape tweened.

Step 3 - Still on Layer two add a second Keyframe in the same frame as the second Keyframe on Layer one. On the Stage place a Frog over the word My. If you have grouped your frog you will have to break it apart before you can shape tween it.

Click on a frame between your two Keyframes and add a shape tween.

Play your movie.