interface(utility and how use that)

If you want to achieve run time polymorphism and to create loosly coupled components at that time you can go with the interface.

I'm not sure what you meant by "utility". Did you meant "purpose" or "use" of the interface, if so you can get the answer in the above lines itself.

Let me know if you need any thing more.

Hi,

Please go through below articles for more details -

http://www.c-sharpcorner.com/UploadFile/sekarbalag/interface-best-example-in-csharp/

http://csharp.net-tutorials.com/classes/interfaces/

http://www.onlinebuff.com/article_implementing-interface-in-c-with-an-example_18.html