int : An integer (eg, 3).
Can be a whole number between -2147483648 and 2147483647
float : A fractional (floating point) number (eg, 3.25907).
Can be a number between roughly 1.5 x 10^45 to 3.4 10^38, in floating point format.
String : A sequence of characters (eg, "Hello User 6555")
(no specified maximum length, as far as I'm aware!)
boolean : A true/false value.
Can only contain either the value true or false.