Masking allows you to hide part of an object or text. It can be used for making
spotlight kind of effects.
Open a new file. On the Properties panel (Window>Properties if it is not visible) make the stage 550 by 100 by double clicking on the Size button to open the document size dialog box. Set the background
to any color you want.
Rename the layer to mask by double clicking the works Layer 1 and typing in the text.
Draw a circle any color on the far left side of the document. We will eventually mask the circle so the color does not matter:
Click the circle with the selection tool . Convert the circle to a symbol by clicking Modify>Convert to Symbol. By converting to a symbol Flash groups the shape. In order to create a motion tween objects must be grouped. Name the symbol circle and click motion clip as the type.
Insert a Keyframe at frame
40 by right clicking in the frame and selecting insert keyframe.
In frame 40 move your circle to the far right side of the stage.
Click anywhere inbetween frame 1 and 40:
On the Properties panel select motion from the tween options list:
Click back in Frame 1.
Lock the mask layer by clicking the dot below the lock on the timeline:
Add a new layer by clicking the new layer button on the Timeline:
Name this layer text. Make sure you are in the first frame of the text layer. Using the text tool , insert some
text into the first frame of this layer. I recommend a thick font like Arial
Black, size 48. Select the Free Transform tool and enlarge the text to fit the stage.
The last step is to create the mask. Make sure the text layer is the top layer!! Right-click on the top layer (text) and select Mask from the menu. Play the
movie to see the results.
. Convert the circle to a symbol by clicking Modify>Convert to Symbol. By converting to a symbol Flash groups the shape. In order to create a motion tween objects must be grouped. Name the symbol circle and click motion clip as the type. 
and enlarge the text to fit the stage. 
