When a DNS client sends a request to a DNS server, the DNS server checks to see if it is authoritative for the zone (domain) in the request or the request has been cached and if so, returns the response
When a DNS server is not authoritative for the specified zone it begins the recursion process.
When the local DNS server cannot server the client DNS request, it sends the request to ROOT server on top, ex: .COM, the root retrieves number .COM domains. From that we chose xyz.com and are forwarded to recursion server.
Once the recursion process is finished, the xyz.com info is cached in local DNS server.