With Astra you get three Sidebar options; viz. the right sidebar, left sidebar and an option that disables the sidebar. You can manage Sidebars in two ways.
- Globally for the site from Customizer
- On particular Pages and Posts
You can find settings under Appearance > Customize > Sidebar
You can set a sidebar for the entire site with the 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.
Astra also allows you to manage sidebars for a particular page or post through the meta settings.