Have you read the wiki?
This is a good starting point.
The config is really straightforward, it is just a xml file with self-descriptive tags. Once you understand how the server works it’s simple to understand.
If you struggle to edit the config file, I recommend you to use a front end for that matter.
If you use version 2.1 or older, CasparCG frontend will work
http://casparcg.com/download.html
If you plan to use version 2.2 or newer, you can take a look at this post.