With Online Store 2.0 and compatible themes, merchants can add sections directly to Blog post templates.
By default, all blog posts will be assigned to the Default blog post template. Create templates and assign them to blog posts to have distinct sections for different blog posts.
In order to add sections to this template, first confirm you are using a compatible version.
Compatible Theme Versions
Add a section to the default template
In the theme editor (Customize), use the page selector to open Blog posts, then Default blog post.
In the left sidebar, click (+) Add section.
Select one of the available sections. Use the search field to search by section name.