Okay. ftp://, http://, https:// are associate with protocols that operate on a common port. You can execute “cat /etc/protocol” (on macOS or Linux terminal) and see each associate common port and their protocol name.

The protocol is associated with a port that is open on a host, which is associated with a process in the OS and that process listens and “talks” those ways when a host connects with a client, like a web browser.