The GraphQL API built with Django and Graphene provides a simple and flexible way to interact with the data model using GraphQL queries and mutations. It allows clients to define the structure of the data required and returns only the necessary data, preventing unnecessary data from being returned. The API includes three primary operations: Queries for reading data, Mutations for writing data, and Subscriptions for automatically receiving real-time data updates. The schema serves as common ground between the client and the server. The API can be tested using tools like GraphIQL and Postman, allowing developers to send GraphQL requests with queries, mutations, or subscriptions.