you can watch these first
http://weelookang.blogspot.com/2011/02/easy-java-simulation-tutorial.html
or
http://www.um.es/fem/EjsWiki/Main/Webcasts

i am not sure if i can find time to make video tutorial.

maybe i try if time permits


your question:
to make the perfume particles come together,
u can try to change the codes to instead of random start positions

to a fix position of your choice

try it and let us know if you are progressing :)