I believe this and this is the information you're looking for.
It's called Stateless Address Autoconfiguration (SLAAC). Basically IPv6 (unlike IPv4) has autoconfiguration protocols in the absence of a DHCP server built into its design.
In IPv4, if a network adapter is configured for DHCP but no DHCP server responds, it will auto-assign itself an address of 169.254.x.x(/16). This is called a link-local address. Any computer using a link-local address can communicate with other computers using link-local addresses if they are on the same network segment. The key here is that link-local addressing is not a part of the IPv4 spec; it's a de-facto standard popularized by Microsoft.
For IPv6 networks, in addition to the link-local address, you also have SLAAC. In a routed IPv6 infrastructure, routers can supply clients with network info via ICMP the way a DHCP server normally would. And since IPv6 has these protocols built into the spec, any IPv6 router would support these requests from clients if configured to do so.
Also, the IPv6 address space is so incredibly big that clients can randomly assign themselves addresses with little risk of collision with other hosts.
In this way, an entire IPv6 infrastructure could conceivably auto-configure itself entirely without any kind of IP address management system.