The layout settings control the page layout. The page is divided into rows, and in reach row is a group of regions.
Select row layouts from the options drop list. Visual sliders show each regions width and position.
You can set a different layout for each breakpoint. Breakpoints allow for different layouts in different size screens, such as mobile, tablet and desktop.
Creating new regions requires editing a simple text file and adding row and region declarations.
Template Suggestions are used to set layout for either a particular page in the site, e.g. the front page, or a group of pages, e.g. all forum pages.
The max-width settings allows you override the page max-width and/or each row width. You can easily set one or more rows to be full width, while others have a constrained width.
When you save a layout a new page.html.twig file is generated along with an updated theme-name.info.yml file. You can backup the existing files automatically.