1. In your document, draw or import the artwork you want to
use as a particle.
2. Convert the artwork to a symbol (press F8), give it a linkage
identifier, and set it to export in the first frame. After you
press Ok you can delete the movie clip from the stage, it will
be used directly from the library. (HINT: In general it
is best to set the registration for the movie clip to the center,
that way the particle can be rotated on it's center)
3. Now that your artwork is prepared, select the component
on the stage and switch to the Particle panel. Set the Particle
Type to "Custom" and then type the linkage name that
you gave to the particle artwork.
4. Publish. You should now see your artwork being spawned
as particles
5. At this point it's up to you to do something cool with
your particles. As an example, I did the following with two
custom particles and some simple ActionScript. You can find
the tutorial that describes how I achieved this effect in the
Tutorials section.