log in to remote machine | SSH

Remote meaning, not the same computer you keyboard is directly connected to. 

We are going to say that the user name for this machine is "serverman"

From terminal
ssh username @ address of your machine
If it is a part of your local network it might looks something like.
ssh serverman@192.168.0.0

If it is public and out of your network, it might look something like
ssh serverman@172.217.164.100

IF the computer is public, AND you have a domain name. You can use the domain name all the same. 
ssh serverman@www.google.com

(I cant really SSH into there. This was just an example...)