I want to create an application.
It is about dealing with files and folders.
I want to create a command which will appear after right-clicking any file on Windows.
Is there any way to accomplish this by C#?
Or do I need to use a lower-leveled language to access those things?
Yes, you can certainly write Windows “shell extensions” in C# or any other .NET language. It is quite involved (have to write a Component Object Model (COM) DLL). There is a tutorial on it using the .NET 4 Framework: http://blogs.msdn.com/b/codefx/archive/2010/09/14/writing-windows-shell-extension-with-net-framework-4-c-vb-net-part-1.aspx