how to use include in php

1<?php
2	include 'archive.php';
3?>

1// Include a file, if it can't be found: continue.
2<?php
3include 'mainfile.php';
4?>
5  
6// Alternatively: Require a file to be imported or quit if it can't be found
7<?php
8 require 'requiredfile.php';
9?>

1// Require a file to be imported or quit if it can't be found
2<?php
3 require 'requiredfile.php';
4?>

1<?php
2     include 'config.php';
3?>