We create our c# dll file using the visual studio 2010.

So first from file menu select the project option, then
select the class library,named it as you wish after cliking ok by default a classlibrary1 has created and inside that a class1 also created.

Inside this class1 you should placed your methods which you wish to use in other project files. After creating the class you should build it.To build it you must save...