Customize Layouts for Blog:

1. Customize Layout for Single Post

Check here and see the post detail with sidebar:

Add Sidebar Layout for Single Post:

Admin -> Appearance -> Customize -> Widget

Here you can drag n drop the available widgets such as Search, Category, Recent Posts, Tag Cloud to "Single Posts Sidebar"

2. Add Sidebar Layouts for Blog Page

Admin -> Appearance -> Customize -> Widget

Same steps you can edit drag n drop widgets to setup layouts for blog category.

After setting, you will see the layout for blog page:

3. Customize sidebar on Left/Right:

Dashboard -> Customize -> Blog -> Archive

• Sidebar position: Set left/right sidebar:

Then the sidebar displays at frontend.