[dba-Tech] Question about Ports

I don't understand the concept of Ports except in the most basic sense. IIS
for example "Listens" on Port 80 by default. So if I switch the Port number
to, say, 8080, do I have to adjust senders to recognize this new port
assignment?

My situation is this: I run IIS on port 80 and Reporting Services works
fine. But then I also do some stuff in Ruby On Rails and its Apache server
also wants port 80. If I change the port number on one or the other web
server, do I have to communicate this info to the dependent programs, and if
so, how?

I hope I'm making this clear. What I do currently is shut down IIS before
switching to RoR, and I would much prefer to skip this step so that both
could run at once without collisions. In the RoR installation, Apache
listens on port 80. Would I have to inform MySQL to address a new port
number? I can see in the .conf file that it's easy to change the port
number. The part of the puzzle that I cannot fathom is how the Sender knows
what port to send to.

TIA,
Arthur