Or you can do right from your command prompt, but first you must edit your Environment variables on your System Properties in Advanced tab then find where `Path` is located and try adding this to the end:
;C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727
Note: that ; is the separator between other paths included in Path environment variable.
and then you can compile your .cs file like shown below:
csc /target:exe yourFile.cs
P.S: .NET Framework version can vary, for that reason i marked Bold and Italic.
Regards,
Milot