How to use a hook?

[dutchbb]

Hello,

Instead of editing a template every time i've done an update, I would like to use the hook system so this is done automatically. But I'm not sure how I can use this system.

For instance, let's say I want to include some HTML at this hook location: $template_hook[postbit_user_popup]

I would also like to use the <if condition=" statement in the hook...

How could I achieve this then?