Php With My Sql(shopping Cart)

am an ethiopian guy computer science student and i prefer a topic shoping cart (on line book sell)for my final project and while i am coding such type of message is comming in diffrent pages "session_is_registered() is deprecated in C:\wamp\www\projc\proj\muk\unprotected 24\user_auth_fns.php on line 45".why it says deprecated and what does it mean?
is there any one helping me to tell me about what kind of error i made on my coding besides anyone willing to help me my project here is my email address eyuel2004@yahoo.com