How to search text using php if ($text contains "World")

What you need is strstr()(or stristr(), like LucaB pointed out). Use it like this:

if(strstr($text, "world")) {/* do stuff */}

In your case you can just use strpos(), or stripos() for case insensitive search:

if (stripos($text, "world") !== false) {
    echo "True";
}