What is cname and PTR record ? And how DNS resolved IP to name and name to IP ? And which process ?

A CNAME record or Canonical Name record matches up a domain (or subdomain) to a different domain. With a CNAME record, DNS lookups use the target domain’s DNS resolution as the alias’s resolution

A PTR record or pointer record matches up an IP address to a domain (or subdomain), allowing reverse DNS queries to function. It performs the opposite service an A record does, in that it allows you to look up the domain associated with a particular IP address, instead of vice versa.

CNAME is a canoonical name record is provide to user fully domain name.Within DNS, an IP Address can be stored against a PTR record. You can use NSLOOKUP to resolve both hostnames and IP addresses, though use of NSLOOKUP has been deprecated for quite some time.