Go to Extensions → Template Manager → (J15) rt_radiance_j15 or (J17) rt_radiance. Mouseover the labels to view a description of each parameter.
There are several sites which offer a range of useful resources for using Joomla, beyond the specifics of the template:
Download and install the Bundle file if Gantry is not installed, use the Standard Template file if Gantry is already present.
Deploy a replica of the this month's demo with ease, using the readily available RocketLauncher package.
All demo content is for sample purposes only, intended to represent a live site. Download a launcher pack to copy the demo.
Joomla.org is an invaluable resource for general instructions and information on how to use, configure and modify Joomla.
More extensive details of the Gantry Framework, inclusive of both written and video tutorials, please visit the dedicated Gantry Site.