How to remember , What sort function doing ( php )

<?php

	$soups = array (
	 'Amiche'  => 'Tomhaar',
	 'Monday' => 'Clam Chowder',
	 'Tuesday' => 'White Chicken Chili',
	 'Wednesday' => 'Vegetarian'
 	);

	$soups2 = array (
	'Thursday' => 'Chicken Noodle',
	'Friday' => 'Tomato',
	'Saturday' => 'Cream of  Broccoli'
	);

	/*

	$arr = $soups + $soups2;

	var_dump("arr" ,  $arr);

	*/

	$arr = array(4 , 1 , 9 ,-1 , 5);

	 // Read as value se reverse sort preserve key values
	arsort($soups);

	var_dump($soups);

	//Read as key se reverse sort , preserve key values
	krsort($soups);

	var_dump($soups);