Any Good Documentation on How Tab Groups Work?

Just went through a real eye opener on tab groups, and I'm still not really understanding their fundamentals.

For instance, in the code segment below (from the post here http://developer.appcelerator.com/question/106601/tab-wont-fire-original-function-assigned#188041), why don't you have to do a win.open() at the end of the function? Sorry for my ignorance in advance:

var win = Titanium.UI.currentWindow;
win.barColor='#007C28';
var webview = null;
webview = Ti.UI.createWebView();
webview.url = 'html/aboutus.html';
win.add(webview);