Where to start learning DirectX technology?

Hey everybody,

I see a lot of talk on the forums about DirectX11 and 12 as of late and the graphics pipeline in general. This is an area that I am sorely lacking in. I have some general knowledge of the graphics pipe line, but nothing specific. I have some questions; one of which is, how will a knowledge of DirectX technology affect the game development process and how necessary is it. Also, can anybody recommend some good starter books for this technology?