Imagine you need to go see your doctor. They work in a building with 65535 rooms. Some rooms are empty. Some rooms have people in them that provide different services. But you need your doctor so you look up their location.

You learn the building address (IP address) and the room number (port)

In practice, you attach services to specific ports so that other computers can access those services. Typically, http traffic is on port 80 and https is on port 443. So if you visit a website, you are likely connected to a server on one of those two ports. But it’s not a requirement. You could create a website and put it on port 2097, or 532, or 47210; it doesn’t matter.

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”.