The layout of the website sets the areas of the website in which content can be inserted. These areas include headers, footers, sidebars, and main content areas of the website. The widths and images of these sections are controlled by the theme, but the layout is what determines if the section will be included and what blocks will appear in that section.

Layouts can be modified in the following ways: 

1. Create Columns -- The Container Block can be used to create columns within sections that already exist. See: Create Columns
2. Select a Different Layout -- Layouts can be changed in a website much like switching the faceplate on a cell phone, it does not affect the content (but some content might not be displayed if it is in an area such as a sidebar that is not in the new layout), and it can be reversed at any time. See: Select a Different Layout
3. Set a Per-Page Layout -- The layout can be changed for just one page of the website. See: Set a Per-Page Layout
4. Adjust the Layout -- The areas in the website in which content can be inserted within headers, footers, and sidebars can be adjusted via overrides from the Appearance / Layout Content screen. No technical skills are required for this operation. See: Adjust the Layout
5. Create a Custom Layout -- More advanced changes may be made by creating a custom layout. Doing this, however, requires knowledge of HTML. See: Create a Custom Layout