Creating multi dimensional array is very easy and it is same as creating single dimensional array. Because array can hold any type of object. It could be primitives or it could custom objects. So, it can hold another array as well.
Example two dimensional array:
$_MultiDimensionalArray = array("Microsoft" => array("C#.NET", "VB.NET", "ASP.NET"),
"Google"=> array("Analytics", "Cloud", "BigQuery"));
echo $_MultiDimensionalArray["Microsoft"][0];
echo $_MultiDimensionalArray["Google"][1];
above code will print "C#.NET" and "Cloud". Using the same idea, we can create 3 dimensional array also.