You can add a sidebar to any page by going to the page settings. You can also add columns.

Step 1

Go to the Pages tab.

Step 2

Click on the Settings (gear) icon.

Step 3

Next to Content section, indicate whether you want to add a sidebar to this page.

Step 4

Click on Save to add the sidebar, or click on Cancel if you don't want to apply the changes.

 Note: Sidebars can only be used with certain Designs.