GraphQL is an API design approach that uses a single endpoint to handle requests and return only the data specified by the client, enhancing efficiency and flexibility compared to traditional RESTful APIs. It operates over HTTP, typically using the POST method, and supports three main operations: query, mutation, and subscription, allowing for data retrieval and modification. Developers can use various tools and libraries, such as Postman, GraphiQL, and graphql-request, to craft, test, and automate queries. Understanding the schema of a GraphQL API is crucial since requests must align with the data model to function correctly. GraphQL requests empower users to optimize performance by fetching only the necessary data, thereby preventing over-fetching and reducing server strain. Additionally, caching features in GraphQL clients like Apollo and Relay can further enhance performance by minimizing repeated requests. Contentful's GraphQL API provides a practical example of a flexible content platform that allows users to query specific content without building a custom backend, supported by tools that help users understand and utilize their data models effectively.