Read the documentation:
Description
int array_push ( array &$array , mixed $value1 [, mixed $... ] )
Return Values
Returns the new number of elements in the array.
The ampersand, &
, is the reference operator. This means that the function will modify the parameter, as opposed to returning a modified version of the parameter:
array_push($staff_group_arr, "Global", "Managers");
print_r($staff_group_arr);
You can also append stuff the simple way:
$staff_group_arr[] = 'Global';
$staff_group_arr[] = 'Managers';
print_r($staff_group_arr);