Definition #2 from Webster.com:

" the place at which independent and often unrelated systems meet and act on or communicate with each other <the man-machine interface> b : the means by which interaction or communication is achieved at an interface"

.. so what kind of interface are you talking about???

This is still really vague. I''ll attempt an answer... DirectX "interfaces" in several ways. The first and foremost in my mind is that it is a collection of COM objects (called interfaces) that allow for direct hardware access for video, sound, input, and network devices (to name a few). It accomplishes this via several other interfaces -- DirectX Graphics, DirectSound, DirectMusic, DirectInput, DirectPlay, DirectShow (there may be others but I think those are the major ones). To write a program that makes use of these interfaces, you simply include the predefined header file, define some variables, initialize COM, and then initialize the specific interfaces you are wishing to use for your program. The best place to learn the knowledge you need to do all of this is right here on gamedev, and what''s not easily found here can be found with a decent search engine. If you know nothing about programming, do NOT buy a game development book or continue with game development until you have the knowledge of at least one programming language under your belt.

If this did not answer your question, please be more specific with what you''re looking for.

Good Luck.