There is only one console port on all routers / switches, so the mark is console 0. To protect console port from unwanted access, we must configure password on this port:
Router(config)#line console 0
With password newpassword we can set new password for console port, and with login we activate it. Also, we can use no password newpassword to delete password, or no login to disable it.
Do not forget to save new settings.