A port is like an apartment number. Except instead of apartments, it’s just mailboxes. Bob’s mailbox is number 25. If you want to get a message to Bob, uou write “box 25” on the address.
A port number is just an additional piece of info that the operating system associates with a particular program. If something comes in on port 22, the sshd is going to handle it because it’s “listening on port 22”, meaning that it has registered itself with the OS as the recipient of anything that comes in marked “port 22”.
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