how to put something into an array phpo code example

Example 1: php append to array

$myArr = [1, 2, 3, 4];

array_push($myArr, 5, 8);
print_r($myArr); // [1, 2, 3, 4, 5, 8]

$myArr[] = -1;
print_r($myArr); // [1, 2, 3, 4, 5, 8, -1]

Example 2: array push in php

$cart = array();
$cart[] = 13;
$cart[] = 14;
// etc

//Above is correct. but below one is for further understanding
$cart = array();
for($i=0;$i<=5;$i++){
    $cart[] = $i;  
}
echo "<pre>";
print_r($cart);
echo "</pre>";