A Header is an area at the top of a page that typically holds the main navigation menu along with some other information, such as a company logo. It is important not to confuse a Page Header with a Page Head. The "head" tag is an area of a page hidden to the visitor, that calls out various CSS and JS resources to a page.
The graphic below illustrates where in a 'Template' structure your Header would exist and how it would be viewed in the front end.
Where can you find 'Headers'?
From your Site Admin, navigate to Site Manager > 'Headers' in the menu on the left-hand side.