Get the embed code
Go to Leadferno to get your embed code.
Squarespace Installation
Squarespace allows you to add the Leadbox embed code to your website using what they call "Code Injection".
To add custom code to code injection:
In the Home menu, click Settings, click Advanced, then click Code Injection.
Add valid HTML or scripts into the appropriate Code Injection fields for the header or footer for the Leadbox to appear site-wide.
After adding your code, click Save.
If you need further help, here is Squarespace's help guide on code injection.