To work with Json using C#, it is need to use Newtonsoft (.net library). This library provides methods that allows the programmer serialize and deserialize objects and more. There is a tutorial if you want to know details about its methods and usages.
If you use Visual Studio, go to Tools/Nuget Package Manager/Manage Package to Solution/ and type "Newtonsoft" into the search bar and install the package. If you don't have NuGet, this detailed tutorial might help you.