Port forwarding and multiple connections

[JB7 0]

How do port forwarding and multiple connections co-exist?
I would like to port forward to a particular machine, but not sure how to connect the port forward to a nominated connection

[eburom 16]

The port forwarding you set applies to all your connections but DDNS wont work if you have more connections so; if you need to reach a particular machine, have only that machine connected to a particular server and reach the server by its exit IP