Once you set up the Pi-hole hardware and software, as well as configure your router to point to the Pi-hole device as the target for DNS requests, you will also need to configure which domains to block. The Bash script above configures the iptables rules to redirect all DNS traffic (port 53) to my Pi-hole and applies Network Address Translation (NAT) rules to allow for network address masquerading, which is a technique that allows to abstract away the internal network from the public internet by replacing the source IP address with the address of the gateway (your router). Long story longer - the script ensures that all DNS requests (both TCP and UDP) from devices on the network are redirected to the Pi-hole, except for requests originating from the Pi-hole itself.