A symbol is a graphic, button, or a movie clip that you create in Flash. When you create a symbol in the authoring environment, each symbol is given its own timeline. Symbols are very useful and most Flash documents will use multiple symbols.
To convert something on your stage to a symbol, you must first select the graphic on the stage that you wish to convert to a symbol. Right click your selection and choose convert to symbol...
After you choose convert to symbol, a dialogue box will appear.
When the dialogue box appears you should enter a name for your new symbol. Then select its behavior. Look below to see which behavior is used for what purpose.
A graphic symbol is used for creating a static image. We can use a graphic symbol multiple times on our stage. The most typical use of a graphic symbol is in creating a motion Tween. When you create a motion Tween, it automatically converts the object you are Tweening into a graphic symbol.
A button symbol is used to create interactive buttons that can have rollover effects and animation applied to them. Buttons are used to trigger events by the user, an example is having our document link to an external Website. We would use a button symbol and then apply the "Go to web page" behavior to have a user link to a Website.
A Movie Clip is used to create a reusable piece of animation. Movie clips have their own timeline that is independent of the main timeline. You can think of them as a movie playing inside the main movie. Movie clips can be used to create animated buttons.