Assuming you have :But I did not understand this, if I am playing movie through iTunes why would anyone want to use Apple TV in it ? Where does Apple TV fot in this entire scenario? How will it help and what will it do ? Or rather what can it do ?
a) an Apple TV connected to your big TV / home cinema and
b) a Mac with Home Movies / Films in your local iTunes (library)
Then you can simply start a movie on your Mac / iTunes and (wirelessly) send it to your big TV without any Cloud subscriptions or streaming plans and without configuring any network sharing.