To change post list page container layout like which column to show the post list, where to show the sidebar and how much width each of these columns should take etc, please refer to Page layout documentation.
Change Post List design
To change Post list design itself,
Navigate to Customize > Blog Settings > Post List
Select from either List or Grid from the options.
Pro version also enables the Masonry option.
Once you change the Post list layout, the preview reloads and shows the updated layout.
Once the changes are finalized, click Publish button to save the changes.