Apollo GraphOS is a supergraph platform that improves client app's time-to-interactive (TTI) and reduces latency in GraphQL APIs by using the `@defer` directive. The `@defer` directive marks slow parts of a query, allowing them to be delivered asynchronously, resulting in faster TTI and reduced latency. To use `@defer`, you need to connect your GraphQL API to the supergraph, define entities in your schema, and mark slow fields with `@defer`. With Apollo GraphOS, you can improve your app's user experience by deferring slow parts of queries, making it a great tool for reducing latency and improving TTI. The tutorial covers how to use `@defer` with Explorer, a GraphQL IDE, and provides examples on how to implement `@defer` in React applications.