Help with exposure control please...

Hello.

I am an amateur photography who is understanding the basics of exposure so I can learn full control through manual.

I am quite capable of exposing images correctly. But where I am having trouble with is underexposing or overexposing for effect. For example, I want to have my subject matter underexposed, whilst the background is still relatively light. An example I have seen of this, is a bride looking out the window. The bride herself is underexposed, whilst the remainder of the phote is bright and overexposed.

I hope I am making sense Any help and advice would be appreciated.