what is session concept in php?

[BLAZER...!]

plz explain me with a real time example...

[kolibrizas]

Session holds data while unless it ends. It ends if user closes browser or is idle for 30min-1h.
session_start();
$_SESSION['user'] = "Andrius";//in index.php takes the user to session;
when you ask for it in any other page(for example buy.php)
session_start();
echo $_SESSION['user'];//will output you the value Andrius;