You can add content to your sidebar by using a Widget. Squarespace has pre-configured Widgets for blog archives, recent changes, wish lists, custom HTML content and more.

Step 1 - Access Your Administration Area 

Step 2 - Access Your Architecture Area

Step 3 - Add A Widget

Click Add Widget under the Section where you would like to place your new content.

IMPORTANT: Widgets and Pages cannot be placed in the same section.
Use this guide to create a new section if necessary »

Step 4 - Select the Widget Type

Click the type of content you'd like to add.

Step 5 - Configure the Widget

Fill in the configuration settings, then press Create Widget.

Step 6 - Enable the Widget

The new Widget will now be displayed in your list of Pages, Widgets and Sections. Click enable to activate it on your live site, if you're ready for it to be public. If not, no worries, just leave it disabled until you're ready to share it with the world.

Step 7 - Edit the Widget