Unfortunately new Radiance users face a challenging learning curve ahead. Radiance is a command line program, and many new users have no previous experience working at the command prompt. Users first need to learn some basic Unix or Windows cmd or PowerShell commands and scripting techniques in csh, sh, Python, Perl, Ruby, Windows PowerShell or some other scripting language.
If you are a new user, first make sure you've followed all the installation steps. User generated tutorials will help you to learn some of the very basics of using Radiance including working from the command prompt, all the way up to running annual daylight simulation. The book Rendering with Radiance provides excellent tutorials on the older parts of Radiance, as well as advanced documentation on simulation settings and computational methods.