To add Social Media Icons to Squarespace Footer, you need to do these
#1. First, access your edit mode
Suppose your site is: elf.squarespace.com
You can add /config after to access edit mode, so the URL will be:
http://elf.squarespace.com/config
#2. Next, click EDIT on the top left of the site.
#3. Scroll down to the Footer and click EDIT SITE FOOTER
#4. Next, click ADD BLOCK
#5. Next, choose Social Links
#6. Edit and add the SOCIAL LINK, the icon will be shown in the box
