proper exposure with flash

[Tom3]

How do I determine what is the proper exposure with the flash?
Let's say I use the camera's exposure finder to determine opening / speed; I still have to factor the flash in; what is the process to go about this?

Also, If I go in manual, on the D200/SB-600 combo, the camera will can still determine the flash strength; does it essentially set it so that the exposure is correct and match the center of the indicator?

furthermore, when the flash strength is determined, does it take into account the angle of the flash head?

I can't seem to find any explanation about how this works.