I'm trying to set up Merlin server on my Mac to send a GANTT chart to my iPad. I need to open TCP ports 7080 and 7090 for it to work. What's the best way to open those ports?
Have you looked at the firewall settings? (Apple menu -> System Preferences -> Security & Privacy -> Firewall Options...)
There you'll find options to block everything, to permit signed software to open ports to listen, and you can click on the '+' button to add a new application.