you get three Sidebar options; viz. the right sidebar, left sidebar and an option that disables the sidebar.
You can find settings under Appearance > Customize > Layout > Sidebar
You can set a sidebar for entire site with Default Layout option.You can set a sidebar for particular Pages, Blog Posts, Blog Post Archives as well.
When one of the sidebars (left/right) is set, you can adjust its width.
also allows you to manage sidebars for a particular page or post through the meta settings.