Can you add one more 'scene' to this project? The new scene needs to have a button in the menu and when this button is clicked, a new backdrop should be displayed with a different character. The 'back' button should be displayed to link back to the menu scene. Try using your backpack to import a backdrop and character sprite from one of your own projects.
Notice how each of the buttons in this project have two costumes and are programmed to display a 'clicked' costume for one second before the scene changes. This is helpful visual feedback for the user.