Who authorizes delegation of a domain to a DNS server?

Question

Domain Name System

Trying to delve into the network and stumbled on domains. In order for my domain to turn into an IP, it must be delegated to several DNS servers. At the same time, as I understand it, I can specify absolutely any servers as dns servers, incl. the registered domain itself (Why?).
1. Why hosting a domain on a DNS server does not require permission from the DNS server admin and why is it free to maintain my domain on a DNS server?
2. The DNS servers themselves are indicated by servers in the form of domain names (ns1.domen.com), then which DNS points to them?
3. Why, if I purchased a domain + hosting, then when I go to the IP address specified in the domain settings on the hosting, I see not my site, but the hosting page "This domain is parked by %hosting name%"? How do they determine that I went by IP, and not by domain name?

Answer 1

Why hosting a domain on a DNS server does not require permission from the DNS server admin and why is it free to maintain my domain on a DNS server?

Why do you think so? Placing a domain on a DNS server is possible only by the owner/administrator of the server. And, in addition to geographic domains of the third and higher levels, it costs as much as the owner requests.

The DNS servers themselves are indicated by servers in the form of domain names (ns1.domen.com), then which DNS points to them?

tree structure. There is a group of root servers that store the data of the first level name servers. First-level name servers store data for first-level domains and second-level servers, and so on. When you query ns1.domen.com, your DNS server receives from the root server the address(es) of the owner of the com zone, from it the address(es) of the owner of the domen.com zone, from it the address of the server ns1.domen.com.

Why, if I purchased a domain + hosting, then when I go to the IP address specified in the domain settings on the hosting, I see not my site, but the hosting page "This domain is parked by %hosting name%"? How do they determine that I went by IP, and not by domain name?

Host header: in the HTTP request.