How do I make a C# DLL?

How do I make a C# DLL?

Use the /target:library compiler option.
In Visual Studio,

1. open the Project File's property page;
2. open CommonProperties -> General -> Output Type;
3. change the output type to class library;
4. build the application to create a .dll file.

Set the path where the .dll file is to be stored by setting Configuration Properties -> Build -> Output Path.