Disney+ is a subscription video streaming service built around Disney, Pixar, Marvel, Star Wars, National Geographic, and wider Disney-owned entertainment. In practical terms, it is sold as paid subscription access rather than a permanent free tier, so the product is not just the catalogue itself but the way the service packages access, apps, features, and account rules around that catalogue.
The point most consumers need early is that Disney+ is an access service, not a permanent ownership product in the old retail sense. You are paying for the right to use the service on supported devices under the current plan rules, not buying a library that sits outside the platform altogether.