Interface is a contract that defines the signature of the functionality.So if a class is implementing a interface it says to the outer world , that it provides specific behavior .
If a class implements a interface then it has to provide implementation to all its methods.
Note:- In CD sample “WindowsInterFace” is provided , which has a simple interface implemented.
Public Interface IInterFace
Public Class ClsDoSomething
Public Sub DoSomething() Implements