Themes are like "skins" for your UB WordPress site. Different themes have different colors, and provide different looks for your site's title, navigation, posts and so forth.
We recommend you start with one of the provided UB-customized themes. These themes use UB's, colors, fonts and have the official UB banner across the top. You can always customize your theme with CSS for a more distinctive look.
UB WordPress themes will also look great on a smartphone or tablet. You can get a preview by loading up your site in your browser, and then resizing your browser window to make it narrower. You'll see your site layout change to resemble the way it will appear when viewed on a mobile device.