<?php
function sum($x,$y) {$z=$x+$y;return $z;
}echo "5 + 10 = " . sum(5,10) . "<br>";
echo "7 + 13 = " . sum(7,13) . "<br>";
echo "2 + 4 = " . sum(2,4);
?>

http://www.w3school.com.cn/php/php_functions.asp