hello.. im new to NAS.. i wanna buy WD mybook live 3TB.. for home user only..

juz wanna ask, r we can play video when browse through it? no need to download it back rght? if i want watch movie inside de hdd, juz open it in media player or must download it? coz juz now all it seller explain to me i cant understand.. lol.. hope u all can clarify much better., thanx in advance!!