You can add extra content into the blog sidebar in 2 locations. This is suitable for adding a blog roll or an advertisement or other content of your choosing.
To add the additional content:
Click on the Settings link for Blog module
Under the "General" tab, select the "Extra Sidebar Content" section.
You will see two areas, "Sidebar Upper Content" and "Sidebar Lower Content".
Once you have written your additional content, click the save button at the bottom of the module settings page.