A one dimension array would be:
var myArr = new Array();
myArr[0] = "Hi";
myArr[1] = "there";
myArr[2] = "dude";
alert(myArr[1]); // Alerts 'there'
A two dimensional array would be:
var myArr = new Array();
myArr[0] = new Array("Val", "Va");
myArr[1] = new Array("Val", "yo");
myArr[2] = new Array("Val", "Val");
alert(myArr[1][1]); // Alerts 'yo'
A 3D array is more complicated, and you should evaluate your proposed use of it as it has a limited scope within the web. 99% of problems can be solved with 1D or 2D arrays. But a 3D array would be:
var myArr = new Array();
myArr[0] = new Array();
myArr[0][0] = new Array()
myArr[0][0][0] = "Howdy";
myArr[0][0][1] = "pardner";
alert(myArr[0][0][1]); // Alerts 'pardner'