When you click the Page tab, the header automatically switches to the Ribbon, and you can begin editing your SharePoint page. To flip back to the standard header, click the Browse tab. The Ribbon was introduced in Microsoft Office and is a convenient way to display many menu items in a small amount of screen space.The Ribbon in SharePoint 2016 features menu items that are relevant to the kind of page you’re viewing, arranged in tabs. For example, the home page of a team site displays two tabs: Browse and Page. You find most of the menu commands you need to use on the Ribbon, and some Ribbon buttons contain drop-down lists. Here is the Ribbon with the Page tab active.
An app displays commands on the Ribbon that provide additional configuration options. These commands are contextual because the commands that appear depend on the context of where you are in the site. For example, the Document Library app adds a Files and Library tab to the Ribbon, in addition to the standard Browse tab.In past versions of SharePoint, all data containers were a list or library. The list and library are still there, but in SharePoint 2016 they are called apps.