Now that we've got our Unity resources taken care of, let's take a look at some of Microsoft's C# documents at https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/index.
There's a ton of other C# resources, ranging from tutorials and quickstart guides to version specifications (if you're into that), all of which are available at https://docs.microsoft.com/en-us/dotnet/csharp.