If you want to base a new drawing on an existing piece of artwork, you can trace it. For example, you can create a graphic based on a pencil sketch drawn on paper or on a raster image saved in another graphics program by bringing the graphic into Illustrator and tracing over it.
The easiest way to trace artwork is to open or place a file into Illustrator and automatically trace the artwork with the Live Trace command. You can control the level of detail and how the tracing is filled. When you are satisfied with the tracing results, you can convert the tracing to vector paths or a Live Paint object.