This tutorial demonstrates how to use JavaScript to call an API, specifically the SendGrid API, to send emails. With a free plan that includes up to 50 emails per day, users can access the Web API from SendGrid to send emails programmatically. The tutorial covers setting up Node.js and Yarn, registering for a RapidAPI account, obtaining an API key, testing the API with JavaScript using Axios, creating an npm package, accessing the API with JavaScript, and integrating the API into a web application using Express.