The implementation of OAuth scopes using FusionAuth involves creating a third-party application and configuring it as such in the FusionAuth instance. This is done by updating the `Scopes` settings for the application, setting the Relationship to "Third-party", and adding custom scopes as needed. In this example, the Budget Buddy application uses a separate identity provider and requests access to the Change Bank API through OAuth scopes. The Change Bank API checks for the correct Client ID and scope, such as `balance:read`, before returning the user's balance. Once the user grants consent, the Budget Buddy application can read the user's Change Bank balance and perform other actions based on the granted scope.