Confused about directX?

For a while I have been programming in opengl and i recently got involved with directx and i was wondering what it is, well i know what it is but its confusing my knowledges is that it is just a set of libraries that lets you have access to your hardware (video card,keyboard etc.) but whats the difference between dx 9, 10 11 ..... does it just have more capabilities like better lighting algorithms and stuff like that