What is a Wordpress theme?
A Theme can also be known as a "skin" or in its simplest form, the overall design of your website. i.e the colours, the menu design etc
In your Wordpress control panel you can search and download over 1,000 different themes for free or you can ask Teckna to design your own bespoke theme based on your brand / ideas. See the Wordpress Hosting page for more information.
If you want to see some of the free themes, look at http://wordpress.org/extend/themes/
To install a new theme could not be simpler. It is all done inside the online control panel. Search on the theme and then click to install. That's all! no download files or anything technical. You can also install multiple themes and switch between them at any stage and your content is not affected or lost.