How to set up with Custom URL Settings are here
Gitup Pages setting https://github.com/cal-icor/homepage/settings/pages
Squarespace DNS settings https://account.squarespace.com/domains/managed/cal-icor.org/dns/dns-settings
Documentation about how to set up Github Pages https://docs.github.com/en/pages/getting-started-with-github-pages/about-github-pages#types-of-github-pages-sites
Managing a Custom Domain via Github Pages https://docs.github.com/en/pages/configuring-a-custom-domain-for-your-github-pages-site/managing-a-custom-domain-for-your-github-pages-site