Interview Questions - Tutoring Online PHP

Hi my dear friends.

Everybody knows what is cookie and session. But let me tell a truth, most of the beginners don’t know properly what is happening in cookies and sessions and what is the real use .I have taken so many Interviews but none of them given a good answer. I am very much sure you are going to get a good idea about Sessions and Cookies. Let us start our battle.:)

I am explaining only PHP syntax here. But the concept of Cookies and Sessions are same in all Server Side Languages like ASP.NET, JSP,RUBYetc.except syntax and some rules

what is Cookie ?