Note that the Coding Train video uses localhost rather than a hosting service. If you code on your local computer only, you cannot show it off to other people. Here we are using the Ancient Brain server, where you can upload not only your own images but also your own music, as the second World shows.
For you: Go to "My uploads" in the menu and upload your own images and put them on the objects. And upload your own background music. Why not?
A suggested next course is the WebGL course. You can also check out the Starter Worlds and Editor's Choice Worlds on Ancient Brain for inspiration on what to code next. You can Clone and Edit all these Worlds. Happy coding!