It is used to forward connection requests from the WAN port to any device connected to the LAN port.
For example, "HUBBOX Connect X1" is connected to the "WAN" port of your device. User A working in the network connected to the "TCP: 5000" port, "HUBBOX Connect X1" can be connected to the 5000 port of any device with an IP address 192.168.1.135 in the network connected to the LAN port. wants to connect. The NAT setting that should be in this example;
NOTE: Both devices must communicate on the same port.