How to use GUIUtility.hotControl?

I need to block inputs to my game when the player is interacting with GUI, and this GUIUtility.hotControl function seems to be meant exactly for that... however I simply do not understand how to implement it.

To me it seems simply return (and assign?) and ID of GUI element... what steps should I take to make use of this? Am I supposed to assign this to variable and put a check into an update method?... That sounds wrong to me. Please advise!

Also in the description it says "When the user mousedown's on a button, it becomes hot." Should I interpret it to mean that the button becomes hot only AFTER I mouse down? - which means that my mouse-down commands will still pass through the GUI?

Thanks ahead of time :)