Well, you looking at the Documentation for Header.JS. First you need to get the script lib which is located at /header.js. Then, use it anywhere. That's right, anywhere. You should call it when the page has loaded in so the header actually does its thing. Let's look at the default values for the function.
The values can be changed to any of your likings. The header's Z-Index is set to 10000, so putting an element to have a higher Z-Index than that would go on top.