Join Morten Rand-Hendriksen for an in-depth discussion in this video Installing and activating Twenty Thirteen, part of Start with a Theme: Twenty Thirteen.
Twenty Thirteen was released in the summer of 2013, as part of WordPress version 3.6. It is available both for self-hosted WordPress sites, and for WordPress.com. Because it is a default theme, it's directly available from the WordPress dashboard. But, if you have a self-hosted WordPress site, and you don't see Twenty Thirteen, you can still install it, because it's also available from the WordPress.org Themes directory.
To start off, I've created a standard WordPress site with some standard content. Here we have a size, we have chat post's, image gallery's, image post's, video's, and so on. The site is currently running the Twenty Twelve theme, and now it's time to activate Twenty Thirteen. So, I'll go to my dashboard, I can select Appearance and Themes, and this takes me to the theme Management page. Here you can see I already have two themes installed Twenty Twelve, and when I stroll down Twenty Thirteen.
If you don't see Twenty Thirteen in your available theme section, or as the activated theme, you can click on Install Themes, and from here search for Twenty Thirteen. And here you'll see Twenty Thirteen, and be able to install it into your site. Once Twenty Thirteen is installed on your site, all you need to do is click on Activate. The theme will be activated on your site, and when you reload the front page of your site, you should now see this iconic orange header image.
That mean's Twenty Thirteen is now active. Once Twenty Thirteen is installed, we can start configuring the theme itself and our content, to utilize it's features to their fullest.