Sections are the highest element in TheDock templates hierarchy and they can be either unique for a specific template or a module. You can always convert a module to a unique section and vice versa by toggling the 'chain' icon.
Inside the section you are able to define how the included areas will be laid out and you can choose between Grid, Masonry and Carousel.
Inside the 'Styling' panel you can shape a section the way fits you the most. Here you can define the height and the background of a section.