You need to know the position, and the LookAt vector of the object you want to follow.

The math is quite simple, normalise the target objects LookAt vector to get a vector i''ll call ObjLookAt.

Now calculate the cameras position by doing:

CameraPosition = ObjPosition - (DistanceToFollowAt * ObjLookAt);

And set the cameras LookAt vector to

CameraLookAt = ObjPosition - CameraPosition;

This will give you a camera that is always at exactly the same point in space behind the object. To make the camera "flow" you simple introduce variables for WantedCameraPosition and WantedCameraLookAt, and every frame move the Camera Position and LookAt some small amount towards those values.

Good luck,

Alan