This is a simple dns server, you can config it like config hosts file. e.g. with this line in your config file:
then all the A queries for domain *.dev.com will return 127.0.0.1.
For all the other requests, including non-A requests and A requests for domains which is not configured, it will proxy them to a real dns server, you can config these servers like this:
At last, an complete config file:
nameserver 220.127.116.11 nameserver 18.104.22.168 127.0.0.1 product.com.
The only argument is the path to your config file, default to "./hosts".