So if I am creating a game and up to this point have only used javascript. Would I be able to add a new C# script?
Yes, but keep in mind the potential script compilation order issues. Generally you wouldn’t want to mix languages, aside from static library scripts. It’s 99% likely you can just stick with Unityscript anyway instead of having to use C#. Remember that all of .NET can be used in all languages; it’s not limited to C#.
–Eric