Create Plugin

Hi Nicholas,

I need to write a small plugin to execute some code once an order has been made.
Basically once an order has been placed, I need to update a custom table in the db.

I had a look at the 'group plugin' to see if I could figure out how it works, and tried to hack it by adding some code under the function called 'onAfterOrderCreate'.
I am not sure how this plugin is supposed to work to begin with, so it was probably not the best starting point.

Anyway, I do not want to hack a preexisting plugin, but rather create one for this purpose.

Is there any guide to creating such plugins, or could you offer some quick pointers?