What you have linked to is a customized theme that you can download and install on a WordPress site if you set it up through an outside hosting company.
Here at WordPress.com, the Custom Design upgrade can be used to customize the appearance of the themes we provide for you. To install your own theme or to do in-depth customizations of how the layout works requires you to have your own setup where you can install and maintain your themes yourself (WordPress.com doesn't offer that as an option).
One of the differences between the two types of WordPress setups is support. WordPress.com comes with a dedicated support team, including this forum, and WordPress.org support is done on a volunteer basis or if you hire someone to help you. Here is a link that explains a little more about the different types of setups:
And Here is a link talking about how to switch to a WordPress.org setup if you're interested in using the theme you linked to: