Show sidebar in posts of your default wordpress theme
In the default wordpress theme, posts don’t include the sidebar. It is important to include the sidebar in all pages for more organization.
Steps to do it:
1. Go to control panel
2. Choose “Presentation”.
3. Choose “Theme Editor”.
4. At the right, choose “Single Post”.
5. Find this code <div id="content" class="widecolumn">.
6. Replace it with <div id="content" class="narrowcolumn">.
7. Find this code <?php get_footer(); ?>
8. Right above it, add this code <?php get_sidebar(); ?>
9. Save and check the changes.