How does it work? Actually, if the help needs an explanation it's probably not intuitive enough for a user... But for you as a developer some background info might be in order.
There are 2 ways for the helpbox to show up. First, for text/number inputs like text/password/email etc. the box shows up when the focus event is triggered on the element. Second, for inputs like buttons and inputs whose values are changed when clicked, the helpbox shows up when the mouseover event is triggered on the element.