Include and require function in php

Include and Require Function in php programming language. You may see websites on internet and think how you will get design and templates for every page the answer is there is preset template not necessary using include or require you must be using very little bit but there is some kind of way to include this suppose i had two files such as index.php and header.inc.php. Now header.inc.php had html tag <h1> my page </h1> now if i want to create multiple pages with same heading