I can not use classes

Cod:

var _class = function(){
   var value : int;
}

var myClass : _class;

function Start()
{
  myClass = new _class();
}

error: "cannot convert ‘void’ to ‘object’ ".

Try this:

function Apple (type) {
    this.type = type;
    this.color = "red";
    this.getInfo = function() {
        return this.color + ' ' + this.type + ' apple';
    };
}

You can instantiate the Apple class like so:

var apple = new Apple('macintosh');
apple.color = "reddish";
alert(apple.getInfo());

Might be worth you doing some tutorials on Javascript - I’d recommend Codecademy.