Assuming you want each user to have their own home folders, create the user first, then either use RDP or VNC if they need a graphical desktop or if they only need access to files and a CLI interface use SSH and SCP instead. Both of these are probably installed in your distribution already. Their help pages explain how to connect and transfer files between systems.
If your other user is remote over the internet, you might have to use port forwarding or even DDNS for them to connect from a different ISP.
Brian.