Create a page called strpos.php.  Under the h1 place this inside the PHP code block:

$stringToSearch="Do not write my name as fred because it is Fred with a capital.";
$position=strpos($stringToSearch, "Fred");
if ($position!=0){
    echo $position;
} else {
    echo "Sorry the string was not found.";

Read the code and try it (you should get a number).  Note that the search is case sensitive and does not find the position of fred.