Setting Up USS

I suppose you have your modding enviroment set up with Unity and VS, including the MSCLoader template. I recommend using the mini dll found here to set up USS in Unity, as it has no dependencies (except Unity itself), what makes it the most hassle-free way possible.
However, for coding you need the full version from Nexus, which is the same later used in the game. Add it as a reference to your Visual Studio project, and aswell put it into your game mod folder under References.

Now you have everything at hand to continue with Creating an USS Item.