As mentioned in the post about Chicken of the VNC, VNC protocol lets you connect to and control another computer. You can do remote troubleshooting or repair, or simply show someone how to do something. VNC requires one computer to have client software (like Chicken of the VNC) and the other computer to have server software. OSXvnc is that server software.
To connect to and fix my parents’ computer, they had to open OSXvnc. Once it was open and configured, I connected in through their router and fixed up the computer.