Here are some definitions and uses of variables of required types: Integer, Number, Boolean, and String

var x : Number;       // x initially 0.0
var m : Integer;      // m initially 0
var isBig : Boolean;  // isBig initially false
var word : String;    // word initially ""
m = 42;
x = 0.25 * m + 2.1e4;
isBig = x > 1000;
word = if (isBig) "Big" else "Small";

Here is a definition and use of a variable of optional type:

class Foo {
  var zing : Integer;
}
var fu : foo;         // fu initially null
fu = Foo {zing: 17}

And a definition and use of a sequence type:

var names : String[];        // names initially []
names = ['Olof', 'Ellen', 'Steve', 'Claire'];
insert 'Bonnie' into names;  // add 'Bonnie' to the end of names sequence
names[1] = 'Donna';           // set the element at 1 (previously 'Ellen') to 'Donna'

Note that sequences are immutable, so technically, each line above assigns a new sequence to names.