In Theme settings you can configure default layout for your website pages. You can see 3 main types here: Right Sidebar, Left Sidebar and Full Width. All of them were shown schematically for your convenience.
In this menu you can enable/disable breadcrumbs and all the sidebars. These are default settings for the whole website, and they will be applied to every new page you create. You can also set custom layout for any page when editing it.