TLD - Top Level Domain (.com .ml .whatever)

Registrar - NameCheap, PorkBun, etc. Submits your domain.TLD request to a Registry

Registry - Maintains the list of domains for a specific TLD and the server infrastructure to run the TLD

ICANN - Decides who can be a Registry and for which TLD. Not involved in the nitty gritty of individual domain names.

ICANN hands out top-level domains (TLDs - such as .com, .org and .ml), either to organisations or government agencies. They, in turn, hand out secondary domains to companies or regional organisations. For example, the TLD .jp belongs to the Japanese government and is operated by an agency called Japan Registry Services. In turn, it hand out the .tokyo.jp secondary domain to the Tokyo Metropolitan government. They, in turn, manage domains for various departments, wards, etc.

But individuals and businesses in Tokyo can also use the .tokyo TLD, which is owned by a private company called GMO Internet Group. And of course anyone can use .com or .org, although you may have tp pay a pretty big fee.