Glad you've got things going well so far. To do what you're looking for, there are a few options.
The main thing that you'll want to do is create a Joomla article (or some other content type item) that is you're 'teaser' intro. That can have your content and links to your website and whatever else you want to entice the user. No, assuming that's a Joomla article, you could reach that article at a URL like (where 5 is the ID of the article):
http://yoursite.com/index.php?option=com_content&view=article&id=5
Now, to get ridof your template and other items and make it just the article, there are a few options:
* You can create a special menu item for that article and then set no modules to show on it. In that case, the URL would use an Itemid (the menu item ID), like:
http://yoursite.com/index.php?option=com_content&view=article&id=5&Itemid=22
* You can use the URL with &tmpl=component on the end, like below, which will show just the article contents:
http://yoursite.com/index.php?option=com_content&view=article&id=5&tmpl=component
Once you decide the look that you want to go for and have things setup, you just need to go into the Autotune Configuration tool -> Facebook App section and then the Page Tab area. Update your Page Tab and Secure Page Tab URLs to whichever URL above that works for you.
Then, whenever anyone sees your Page Tab 'home page' it will be the intro URL you created and not just your home page.
Whew.. I hope that helps explain, but if you have any questions, just let us know.
Thanks,
Alex