Classes are not very important. They are over hyped. They can be very useful for some things but you never really NEED them. You certainly shouldn't use them for everything. That's all hyped-up bullshit.
I learned Direct3D and DirectInput from these sites:
I would recommend learning OpenGL instead of Direct3D though. Direct3D is a lot harder to understand. I mean A LOT.
DirectInput is good though. Well. It's hard, but it is good to know.