To add a Shopping Cart icon to Squarespace, you can follow these steps.
#1. Access edit mode and click EDIT
#2. Hover on Header and click EDIT SITE HEADER
#3. Click ADD ELEMENTS
#4. Click Cart to enable it
#5. Cart will appear, click it and click Pencil icon to edit Cart
#6. You can choose Cart icon style here
Squarespace provides these styles.