Templates control the appearance of your website.
This blog is installed with the Protostar template.
You can edit the options by clicking the Working on Your Site, Template Settings link in the top menu (visible when you log in).
For example, you can change the background color of the site, the highlight color, the site title, the site description, and the title font used.
More options are available in the site administrator. You can also install a new template using the Extension Manager.