What is the difference between a registry and registrar and registrant

Registry Registrar and Registrant definition

in registration process there are three different roles that associated with this process
The registry, registrar, and registrant. The following describes each role and how they work with one another:

Registry: A domain name registry is an organization that manages top-level domain names. They create domain name extensions TLD, set the rules for that domain name and what the features for this TLD, and work with registrars to sell domain names to the public.
An expample : VeriSign manages the registration of .com domain names and their domain name system (DNS).

Registrar: The registrar is an delegate organization, like XsoftHost , that allow to sells domain names to the public . Some Registrars have the ability to sell top level domain names (TLDs) like .com, .net, and .org or country code top level domain names (ccTLDs) such as  .ca, and .eu.

Registrant: A registrant is the person or any company who orders and  registers a domain name. Registrants can manage their domain name’s settings through their registrar (Xsofthost).

When any changes are made to the domain by registrant like contact informations and/or DNS , Nameserver ,Lock domain, their registrar will send the information to the registry to be updated and saved in the registry’s database.
So when you order and register a domain name, you become a registrant