The Composition API is a new way of writing and organizing code for building Vue applications, offering flexibility around how code is written while maintaining legibility, readability, and ease of maintenance. It provides reactive and ref helper methods to make data reactive, allowing developers to create more dynamic and interactive user interfaces. The API also includes computed properties, which can be used to calculate values based on dependencies, making it easier to perform complex calculations and updates. Additionally, the Composition API allows developers to define methods, which are regular functions that can be called from the template, and serverless functions, which can be used to run server-side operations without maintaining a dedicated server. The Composition API is particularly useful for building dynamic Jamstack applications, where serverless functions can be used to perform server-side operations such as authentication, validation, and data storage.