The tutorial covers the implementation of GraphQL subscriptions on the client-side using Apollo Client, allowing instances of the client to see live updates to messages in a channel. The process involves setting up a WebSocket connection between the client and server, constructing a subscription client, and merging it with the existing network interface. The client then uses subscriptions to detect the creation of new messages and update its React views accordingly. To prevent duplicate messages, the application checks for the existence of the message in the store before adding it. With this implementation, multiple users can see each other's changes in real-time.