How to create drawing substitutions?

My problem is very simple (and the answer most propably :-[) But I have tried in many ways to create drawing substitutions of symbols, but I haven’t succeed in that. Also I have failed to find instructions to do it. So could someone please help me.

God Bless,
petrip

To add extra drawings:

1. In the Camera view, double-click on the part to which you want to add a new drawing to edit the Symbol.
2. In the Timeline view, select the cell where you want to add your new drawing.
3. In the Tools toolbar, select the drawing tool you need to draw your extra part.
4. In the Camera or Drawing view, draw your new drawing.
5. Using the Select Tool, select your drawing and flatten your lines by clicking on the Flatten Button
In the Camera view, click on the Top Button to go back to the root timeline.

Regards
Nolan

adding to nolan’s post:
ad 3. be sure to check out the ‘animate’ button, otherwise you won’t be able to draw in the camera view

check the video tutorials at justin’s page, there are some substituton drawing issues:
http://cartoonsmartblog.wordpress.com/2009/02/06/free-toon-boom-animate-lesson-on-hierarchical-character-rigging/
rob