1 ) the bit before the => is the key, the bit following the => is the value.
2 ) Yes, associative
2b) indexed, or numeric, arrays
2c) But they can be mixed, for example
$arr = [ 'This is a key' => 'This is a value',
42 => 'second value',
'Third value'
];
echo $arr['This is a key'] . '<br>';
echo '<pre>', print_r($arr, 1), '</pre>';
which outputs
This is a value
Array
(
[This is a key] => This is a value
[42] => second value
[43] => Third value
)
3 ) I think the above example answers that.