I'm new to Titanium, and am having a problem with navigationGroups I cannot figure out. I'm sure it's just me being a noob, and should be a simple fix. I just need an explanation.

I am building an app that starts out with a window (app.js) that has no tabs, only buttons. When I click a button, I want the next window (about.js) to use a navGroup, so the About screen 'slides' in. I just cannot get this to work. Guess I just don't understand how navGroups work. Any help is greatly appreciated. I've looked at the examples in KitchenSync, and still can't figure it out! Do I put the NavGroup in app.js, or in about.js?

Here's my code:

app.js:

// this sets the background color of the master UIView (when there are no windows/tab groups on it)
Titanium.UI.setBackgroundColor('#000');

// create root window
var rootWin = Titanium.UI.createWindow({
backgroundColor:'#000'
});

// create main window
var mainWin = Titanium.UI.createWindow({
backgroundColor:'#000',
backgroundImage:'images/background.png'
});

// add the about button
var aboutBtn = Titanium.UI.createButton({
title:'About',
color:'#ff6',
font:{fontSize:15, fontWeight:'bold', fontFamily:'Helvetica Neue'},
backgroundImage:'images/button.png',
top:110,
height:34,
width:160
});

var aboutWin = Titanium.UI.createWindow({
url:'subWindows/about.js',
title:'About'
});

aboutBtn.addEventListener('click', function(e){
aboutWin.open();
});

mainWin.add(aboutBtn);

// open the root window
rootWin.add(mainWin);
rootWin.open();

about.js:

// this sets the background color of the master UIView (when there are no windows/tab groups on it)
Titanium.UI.setBackgroundColor('#000');

// create root window
var rootWin = Titanium.UI.createWindow();

// create main window
var mainWin = Titanium.UI.createWindow({
backgroundColor:'#000',
backgroundImage:'../images/background.png'
});
// ———————————————–

// create the navigation group
var navGroup = Ti.UI.iPhone.createNavigationGroup({
window:mainWin
});

rootWin.add(mainWin);
rootWin.add(navGroup);

// open the main window
navGroup.open(mainWin);