I can't figure this out.

[Ghosty]

You can't add a solely horizontal tiled image to the terrain, AFAIK, but you can add vertically and horizontally tiling images -- the Terrain.Image property.

As for making a platform with rotatable wheels that move on their own:

Pause the game and make the platform, then place two circles on it so that they make decent wheels. Then, use the Hinge tool on the center of the circles -- as close to the center as you can. Then, select the Pointer tool and click on the black hinge circles. In the Properties section, there should be two number properties, one related to motor force and one to motor speed. Turn them up a bit, hit play, and see if the platform starts rolling. If not, turn them up even more. Once you get it working at a good speed, you can drag it back and set up a block in front of it to stop it from moving until you want it to.

And background music is pretty easy. If you want perfectly looping audio, use .wav, but if it doesn't loop seamlessly, like an actual song, use MP3s, for better file size.

Set the Looping property to True and put a script inside the sound object. One line is all you need: script.Parent:play() and you're good.