It’s the one thing when I’m configuring things that makes me wince because I know it will give me the business, and I know it shouldn’t, but it does, every time. I have no real idea what I’m doing, what it is, how it works, so of course I’m blindly following instructions like a monkey at a typewriter.
Please guide me into enlightenment.
A “port” is just a number that gets assigned to network messages to differentiate targets within the same IP address.
One program is “listening on port 1”, which means it has told the operating system “anything labeled port 1, send it to me”.
It’s sort of like saying “attention: Joe” versus “attention: Sue” on an address. Same address, same building, but that “attention” line means to put it on Joe’s desk inside the building.
Except instead of “attention: Joe”, it’s just “attention: 22”. A numerical code that represents a “mailbox” inside the computer.
To take this further, if the office mailroom is the router, opening a port is like telling them “we just hired Jeff, so accept mail with ATTN Jeff” and closing a port is like “we just fired Sam, burn all mail addressed to Sam”.
That is The Good Answer.
Another, very similar way of thinking about it is that It’s effectively like an apartment or office number. A post office typically ignores it, but if told to, they would forward a specific apartment number at a specific address to a new address and apartment number.