Its very simple.
Just save the joinfeeds.php file and then have your test.php be like this

%
<?php
    require_once 'forum/joinfeeds.php';
    $latestfeeds=latestFeed(5);

//Print some stuff from entries
foreach($latestfeeds as $feed) {

echo $feed->link," ",$feed->title," ",$feed->description
}

?>

%

I havent tested the above so experiment and use php.net for help. You have to take a look at the index.xml files to see what is available

:: @Jos added on 25 Jul ’16 · 18:27

Beware of path of require_once 'forum/joinfeeds.php';

:: @Jos added on 25 Jul ’16 · 18:29

And remember this is something that is perfect for me. It does not necessarely something for your setup, but its simple and easy to adapt to your needs. No need to a complex tools when something as simple does the job.