A domain registrar is an entity or organisation accredited by ICANN that manages the registration and sale of domain names.
Through registrars, specifically, users have the possibility of checking the availability of the selected Internet domain, making sure that it has not already been assigned to another web page, so as to purchase it. Registrars in fact have access to registries, databases that contain the complete list of available domain names and information on their owners.
If the availability of a domain is confirmed, registrars release it upon payment and, immediately thereafter, update the information in the registry of the relevant Top Level Domain (TLD).
All data of the user who requested registration (i.e. the registrant) such as e-mail and telephone number will therefore be entered.
You can imagine registrars as a sort of car dealer who, in addition to showing the customer the available vehicle models and finalising the purchase, also acts as an intermediary in case there are problems with the engine. In practice, the sale consists of the conclusion or renewal of a subscription (usually for one year, up to 10) that associates the user’s data with the selected domain.