Creating a product - what variables are available?

[crkgb]

I am trying to create a new product with its own plugins and templates. When I add a new plugin to my product, how do I know what objects are created and available, and what variables are set? The vBulletin manual states:

When adding code to a plugin, you should bear in mind that your code will have access to all variables and classes that are exposed at the point where the hook is placed.

vBulltin API docs provide lots of info on classes themselves, but nothing on what is available at what point?