To remove Header and Footer in Squarespace, you can follow these steps.
#1. Hover on Page where you want to remove Header and Footer and click Gear icon
#2. Click Navigation
#3. Disable both options and click Save
#4. To remove Header and Footer on Cart Page, you will need to use this code to Custom CSS box
body#cart {
header#header, footer.sections {
display: none;
}
}