This tutorial provides a step-by-step guide on building a custom Chrome extension to add a feature to the Daily video call platform. The extension allows users to mark themselves as having gone in a call, without requiring manual updates to the code base. The process involves creating a manifest file, adding content scripts and icons, updating the DOM with buttons for each video participant, and styling the buttons with CSS. Once all the code is written, the extension can be loaded into Chrome by going to chrome://extensions/ and selecting the project directory.