{Phishing} {Disarmed} [CentOS] Trying to understand Remote desktops

I joined this thread a little late, but I have a related question: how
do I log in on a remote machine (assuming that some form of remote
desktop is set up to receive that login on the remote machine) that is
on the other side of a router (i.e., has no internet-visible IP
address)?

Thanks.

mhr