Page sections are reusable content types, that you can use if you find them useful in a variety of locations, or you can completely ignore them and turn them off if you wish.
This functionality is build in into a separate plugin ( named: Pagesections by Develoved ) which is bundled with the theme and can be installed easily through the required & recommended plugins installer ( Appearance -> Install plugins ).
See Installing required & recommended plugins for more.
Examples of where you can use page Sections are in all pages or certain templates by setting the appropriate option throught theme options (see for example, Header->Header Sections in the theme's options panel), right before the footer, inside the footer and/or the socket and in ANY place you can add content using the Visual Composer. Using the Visual Composer you can add a Page Section using the 'Section' element.
You can also add multiple page sections in the 'Sections Slider' element and easily create a simple slider.