The Swift 5.5 language feature async/await is used to improve the readability of concurrent code by removing the need for completion handlers, allowing developers to create more efficient and easier-to-understand asynchronous code. This tutorial demonstrates how to send an SMS message using the Vonage Messages API with Vapor, a server-side web framework built on Swift. The tutorial covers creating a new project, setting up the necessary dependencies, defining routes, parsing form data, making HTTP calls to the Vonage API, and rendering the response in a view.