It sounds like you answered your own question.
Question: X of what? You've got x-position of actor, x-position of background, x-position of mouse hover, mouse click, etc. You also have x-speed, though that would be mathematically messy.
The key to development is experimentation. If you don't know how something works, try it anyways. If it doesn't work, tweak it.
Sorry if I'm not much help, but it's something.