Not sure if this is what you are asking, but when you create an array like this...
$array2 = array(1,2,3);
...the array will be numerically indexed, starting at 0, as if you did...
$array2 = array(
0 => 1,
1 => 2,
2 => 3
);
Therefore, the first $key will be 0, while its associated $value will (initially) be 1.