The website will have a search bar in its header at the top of all pages that searches all on-page content and also directs the user to use the Document Library search (if this feature is used) if they do not find what they are looking for at first.
A search bar can be added to a website at any time if you initially decide against it and then choose to add it at a later date.
Search Field
Search Icon that opens a full page (1), or sidebar (2) overlay
