T4 Framework is the template for the website, your header, menu and footer are designed in T4 framework. T4 Page builder is the content designer that fills in the component section of the T4 framework.
Yes they can be installed together as the perfect pair, but if you are more familiar with another framework like Helix Ultimate to do your Header Menus and Footer then you can use T4 page builder the same way you would have with T4 framework.