How to use System.Configuration.ConfigurationManager in Windows Forms, Console, Class Library and Windows Service Applications in C# and VB.Net

Here Mudassar Ahmed Khan has explained how to use System.Configuration.ConfigurationManager in Windows Forms, Console, Class Library and Windows Service Applications in C# and VB.Net when the following error occurs. The type or namespace name 'ConfigurationManager' does not exist in the namespace 'System.Configuration' (are you missing an assembly reference?)