The project is launched on two ports, for what?

Question

JavaScript

On my project, I run the server on a specific port, and in the browser, respectively, I prescribe localhost:port.
And everything works. Other people, on their own projects, make the server run on one port and the client part on the other, and with the help of a proxy, they make it possible to make requests to the server from the client part.
Question: 1. Is it possible to create two servers? or how does it work on two ports?
2. Why create two listeners, if you can configure everything to listen from one port?

Answer 1

I did not understand what the "client part" is.
1) One server can listen to two ports - for example, Apache.
2) It makes sense to spread different functions to different ports. For example, users go to one port, and the admin - to another. It becomes more difficult for hackers - the second port must be found, the most stupid / inexperienced "mom hackers" (youngsters) break off on this - the most annoying part of hackers. In addition, the admin port can be covered in the firewall - so that there is access from a specific list of IP addresses. Or you can cover it with port-knocking technology.
This is if I understand the question correctly.