Interfaces

Question

Could anyone please elaborate on how to use interfaces in .Net? I know that if I implement an interface in a class, that class should make use of all the members of that interface. But, when I work in .Net (ex: C#.Net), while doing the code, I could see a lot of interfaces like ex: Iinterfacename with a magnifying glass icon. How can I make use of all that? A sample code is well expected. Thanks in advance.