I want to do exactly same device ,please help me .
the examples which are on V-USB have other basis or purposes , and they are very complicated .
what happens if I buy simple USB mouse and interface it with arduino
Making V-USB work starts with programming stand-alone chips.
The hardest part of doing that for me was getting my Arduino-as-ISP to breadboard wiring right. That took me a few attempts alone.
If you're not prepared to bang your head against a seeming wall a few times then get a Teensy of other cheap USB-based-chip compatible with HID library available and count yourself lucky they're available. There's still plenty to do even if all you want is to touch a wire to a pin to move the mouse pointer.