I can hear you asking "what is unity" ? Well here is a direct answer!!
Unity is a GAME ENGINE.
Okay but what is a game engine? (That is the boring part)
A game engine is a system made for the development of games. A game engine provides a graphic renderer, animation, scripting, AI, sound, a physics engine etc... . These things are all used to create a "game".
You can create your dream game using unity. But do NOT and i repeat DO NOT think that you could do it in one month...or even two. Making your game requires passion, dedication, and most importantly TIME! One more very important point do not thing BIG. Start by creating small games! Master unity and then think BIG.