The first thing that we should we familiar with when making animations in flash is the timeline. By the end of this tutorial, you will be familiar with frames, key-frames and the timeline and will be able to create animations of objects using Tweening...
The TimeLine ::
 The timeline is that area where you will be working with layers and frames to alter the movies contents or to animate them.
It also contains info like fps, current frame and length of the movie...

Frames and KeyFrames ::
Keyframes are those frames that define the initial and final postitions of an object in an animation and the frames inbetween are filled by fillers known as frame. A keyframe is marked by a circle (frame 1 in picture) and frames are marked by rectangles...



Tweening :: (in Flash Cs4 and later)
Tweening is a technique employed in animation where intermediate frames are developed inbetween two KeyFrames to create a smooth animation, giving the appearance of the first keyframe evolving into the other.

To create our tweening animation, first launch Flash and create a new file (Ctrl+N) and select ActionScript3 from the list. This should open a new flash movie with a white stage. Now move the mouse over to the timeline and select the first frame as shown in the above picture. Now import an image that you would like to animate onto the stage. To do so select import to stage from the menu (File>Import>Import to stage) or use the shortcut Ctrl+R and select an image.

This should bring the image onto the stage. Select the image and convert it into a graphic symbol (Ctrl+F8). Nowright click on the and select "Create Motion Tween" this should create some frames for the animation as shown...

Now select the last frame and move the image in the direction you want it to move this should show a green trail if done correctly, as show in the image... Now test the movie and you should see your object animate and move. In case you want the animation to last longer or shoter, you can drag the last keyframe to the right or to the left respectively to reduce the movie time...
Now that you know how to tween postition, you can try out tweening other properties like transparency, scale, rotation or even combinations of any to create animations...This can be achieved by setting initial properties in keyframe 1 and final properties in keyframe 24.


For a more detailed description on tweening, try the article:Intro to Animation by kirupa.com