There are three different roles involved in domain name registration and management. That is, the registry, registrar, and registrant. The following information will explain these roles and how they work.
A domain name registry is an organization that manages top-level domain names. They create domain name extensions, set the rules for that domain name, and work with registrars to sell domain names to the public. For example, VeriSign manages the registration of .com domain names and their domain name system (DNS).
In short, registry maintains an authoritative database regarding top level or lower level domains including zone files.
Few registries who manages popular top level domains,
The registrar is an (ICANN)accredited organization, that sells domain names to the public, that is registrants like you. That is, registrar works with registry to sell domains to public.
Few popular registrars are,
A registrant is the person or organization or company who registers a domain name. Registrants can manage their domain name’s settings through their registrar. When changes are made to the domain, registrar will send the information to the registry to be updated and saved in the registry’s database. You become a registrant if you are registering domain name!
You can find registry details of domains at root registry database http://www.iana.org/domains/root/db