I would like to create a new toolbar button on the applications main toolbar and have it invoke a method on the active form. How do I set that up?

I've been doing some investigation, but I'm not sure where I should put the code. Lets say I want to define a new method "mymethod"

.statemanager.DefineAction('Form Mymethod', 'mymethod')

Furthermore, once I get to that point, how will I enable & disable the button from the form level?