Building and deploying a Nuxt3 app on Netlify using CircleCI involves setting up a continuous integration/continuous deployment (CI/CD) pipeline to automate tasks that can't be run directly on Netlify, such as custom scripts and automated testing. Nuxt.js, a framework built on Vue.js, allows for the creation of universal applications, and Netlify serves as a popular hosting platform for Jamstack websites. The process begins with setting up a Nuxt3 application, adding pages, and installing the Netlify CLI for deployment. The tutorial guides users through disabling Netlify's default build triggers to save resources by utilizing CircleCI for deployments instead, requiring configuration of environment variables and updating the CircleCI config file to include deployment credentials. By implementing this setup, developers can ensure that their Nuxt3 app is successfully deployed to Netlify from CircleCI, allowing for more control over the build process and seamless integration with version control systems like GitHub.