If you wish to display a sidebar in your blog overview page or blog posts you need to set this first in Theme Settings > Blog.
After you make your selection you need to add content to the sidebar.
- Go to Appearance > Widgets
- Various Widgets are available for you to include in your sidebar
- Drag and order the widgets you wish to show into the Primary Sidebar.
- Have a look at your blog post to see the results and add or remove widgets as necessary