The GraphQL API allows users to message each other, creating new messages and retrieving existing ones. The server pushes new messages to subscribed clients in real-time using subscriptions. The API uses an asynchronous server built with Uvicorn, a Python library that supports ASGI, and Ariadne, a Python package for building GraphQL APIs. It also uses asyncio.Queue to manage the subscription queues. The client can subscribe to messages for specific users, receiving new messages as they are created. The API includes features such as user authentication, message sending, and receiving, making it suitable for real-time communication applications.