How do I track a model with a cam, only on certain axis

My question is porbably actualy more complicated than the title, probably really stupid, and easy to fix.

Lets say I have a sphere, I now have a cmaera, a short distance away from the sphere. How do I make it so it stays at this angle, and distance from the sphere, but as the sphere turns, as does the camera, and as it goes forward, so does the cam.

A side question:
How do I make the front of the sphere (So pressing forward always makes it go in the direction you are viewing) always follow the mouse, which inadvertantly follows the camera.

I can probably make this a lot easier.

How do I make a camera that is simalar to third person games, that can be controlled by the mouse, and the player model is controlled by the mouse like this too…

I think I said that quite awfully…