When a connects to the network, it requests an address to become part of the network (specifically, an IP address).
The DHCP server responds to that request, giving the device a valid IP address on the network.
During that step, the device also sends information about it to the DHCP server like its’ hostname.
Once the DHCP server finished, it passes this information to the DNS server so anyone asking for that computer by its hostname can access it.
There is also a system within each LibreRouter that syncronizes the DNS information (among other relevant data) between them… so if one LibreRouter knows about a device, all of them will know, so you will be able to refer to a computer by its hostname.
As an example, let’s say we have a computer in our community that has the wikipedia stored inside it. If we give the hostname ‘wikipedia’ to that computer and we connect it to the network, you will be able to access this computer on your browser connected on any node of the network by typing http://wikipedia/ or http://wikipedia.thisnode.info