Hack N' Slash RPG (Diablo-Style) Mouse Targetting?

Hello.I've been working on a small hack n slash rpg game like Diablo, Titan Quest, Torchlight etc but i am seriously stuck at the targetting/attack system. I want to be able to target an enemy just by taking the mouse on him and then press the left-click for example and move for attack. Is it possible to give some tips for it or even a similar code which i can fix by myself? Thanks!