I was looking for a code for a web page which has the functionality wherein some previously registered admins can login and after doing so, they can add, modify or delete data from a product list already available in a database.
This is a very open ended question and there are literally 100s of ways to go about it. You essentially need two systems
The system that allows to Create, Update, Insert or Delete stuff from the database.
One example of that would be http://net.tutsplus.com/tutorials/php/real-world-oop-with-php-and-mysql
Again, it might not be the best or the easiest way. But definitely a place to start.