To understand how the grid layout editor works, we must first understand the structure of the grid layouts.
Grid layouts consists of two main areas that need to be configured, grid layout area and grid rows.
The layout area is where the overall page layout is defined. Layout areas are divided in to layout sections e.g. a sidebar section and content section. The size of the layout sections is defined in columns. For a full-width content area use max number of columns (12 for Bootstrap 3). Each layout section contains one or more rows.
Grid rows is where the actual content goes. Each row is divided into cells that contain the property editors. The size of the cells is defined in columns. Unlike the layouts sections it is possible to add more cells than the max number of columns - they will stack as they should in a grid system.