A small correction: the registrar directs the registry (on your behalf) to configure the registry's DNS servers to point at whichever DNS servers you specify to host the domain, which default to the registrar's DNS servers. The chain of delegation is most commonly either:
root -> registry -> registrar
or
root -> registry -> another DNS hosting provider (CloudFlare, AWS Route53, DNS Made Easy, etc)
A small correction: the registrar directs the registry (on your behalf) to configure the registry's DNS servers to point at whichever DNS servers you specify to host the domain, which default to the registrar's DNS servers. The chain of delegation is most commonly either:
or