Say you have a simple XML file books.xml  that looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<books>
	<book>
		<author>
			<name>Nikola</name>
			<surname>Brežnjak</surname>
		</author>
		<title>Some awesome book title</title>
		<year>2014</year>
	</book>

	<book>
		<author>
			<name>Patrick</name>
			<surname>Rothfuss</surname>
		</author>
		<title>Doors of stone</title>
		<year>20xx</year>
	</book>
</books>

and you want to get all the names of the authors, you can use SimpleXML:

<?php
	$xml = simplexml_load_file("books.xml");
	var_dump($xml);

	$data = array();
	foreach ($xml as $book){
		$data[] = (string)$book->author->name;
	}

	var_dump($data);
?>

The output in this case will look like this: