A responsive page is made up of 4 different components that behave differently depending on how you edit them. A page menu, section, row and column.
To add a section
On the Left Sidebar, select Sections.
Drag it onto the page canvas.
Adding a section will automatically create a row and column.
Tip: When you hover over certain parts of the responsive editor, dashed outlines will indicate these. With a component selected, the component type will be shown in the top left corner of that selection.