Introduction for beginners!

Hi guys,

I am a beginner, is there any introduction for v-usb? all I see is professional instructions!
I have read wiki, comments in usbdrv.h, usbconfig.h and main.c in some example projects, but they seem complicated to me.
I don'n know, for example, which message or data transfer from device to PC or ...

Also, it may be very simpler than what I think. Is it true?
Otherwise, is there a basic introduction explaining v-usb?

Thanks a lot