Click the green flag and watch 'em go! You can freely use this as the background to one of your projects, or as another part of it.
TIP: The backpack function of the online editor can hold more than just scripts, you can put costumes, backdrops, sounds, and even entire sprites (complete with their scripts, sounds, and costumes) into it. If you want to use this in one of your projects, just use the backpack instead of remixing it.