The Daily JavaScript library allows developers to add video calls to their web app with various options for customization. The walkthrough focuses on the fully custom experience using React and the Daily Call Object API, which involves creating a basic video chat web app that can join and leave rooms, render participants' media tracks, and toggle camera, microphone, and screen share buttons. The implementation covers key concepts such as Meeting State, Participant State, and handling edge cases like camera and microphone errors, unsupported browsers, and browser-specific screen sharing limitations.