Flash has three basic types of symbols - graphics, buttons and movie clips. Each has a specific purpose within a Flash movie outlined below. Symbols can be created in Flash by clicking on the object and hitting the keyboard shortcut F8 or using the menu, Modify > Convert to Symbol. Both ways will give you a small dialog box in which to choose the type of Symbol you would like to create, as well as a field to enter the name of your Symbol. Keeping your symbols well organized with specific names will make it easier to find and edit symbols from your library as your movie progresses.

TIP: When edited a Flash file, be careful that you are not mistakenly working in "Symbol Editing Mode". When you double-click any unlocked symbol in Flash, the software will take you into symbol editing mode. At that point, you are editing the actual symbol file. Editing the symbol file will globally change the symbol wherever it is used throughout your movie. An example of what symbol editing mode looks like is outlined in the image below.

Graphic Symbols can be used in Flash to animate picture files (jpeg, gif, png) and text, as pictured below.

Any basic object can be converted into a Button in Flash. This includes shapes, text, picture files (jpeg, gif, etc) and also graphic symbols. Each button has 4 different "functions" that can be stylized: Up, Over, Down, and Hit. The Up function refers to what a button will do when it appears in the flash movie. The Over function refers to how the button changes when the mouse rolls over it. The Down and Hit functions are often times confusing to explain. The Down function refers to the style of the button when a mouse is clicked on the button and held. The Hit function refers to the style of a button right after it is clicked. 

The sample Flash movie below shows examples of these different states of a button. Try to roll over, press down, and hit the button.

Movie clips are the most dynamic symbols in that they can include shapes, text, graphic symbols and buttons. It is helpful to think of movie clips as small movies within your Flash movie. The movie clip below is animating the existing graphic that was created above. The graphic symbol is rotating while the movie clip enables this rotating graphic to move along the page. Movie clips have the most capabilities for dynamic action scripting of all three types of symbols.