Hooks are a feature of action helpers that allow you to automatically run code at certain points in the dispatch cycle. Specially, there are two hook functions available for action helpers: preDispatch and postDispatch. These allow you to ensure that some functionality is always run for each request.
He creates a simple action helper that grabs a random quote from an array and drops it into a property of the helper. By defining a preDispatch method inside of the helper, the HelperBroker knows to pull the method in an execute it immediate before the rest of the actions are executed. A calls to addHelper with the hooks defined is all it takes to glue it together with the execution.