The below example shows a simple port forward that is forwarding TCP, Port 32400 (Plex) to the internal address 192.168.88.250 (Plex Media Server)
This string is entered into the console.
/ip firewall nat add action=dst-nat chain=dstnat disabled=no dst-port=32400 in-interface=ether1-gateway protocol=tcp to-addresses=192.168.88.250 to-ports=32400
