There are three types of symbols. Graphic Symbols, Button Symbols (covered later in this course), and Movie Clip Symbols (covered in the Advanced Course). This lesson primarily covers Graphic Symbols.
Symbols all have their own timelines. In fact, the timeline is one of the biggest differences between the types. Buttons have a special timeline that reacts to the user's mouse (when the mouse is over, for example, formatting can be applied to create an effect). We will see more about Buttons later.
Graphic Symbols and Movie Clip Symbols both have a layer structure and timeline that looks like the main timeline. Movie Clip timelines play independently of the main timeline. But, Graphic Symbols play in synch with the main timeline. That means if the main timeline stops, any Graphic Symbols will stop, also.