an org network is like a network that any VM/vApp can connect to.
if you make an org network, create a vApp and attach the VM directly to the org network.
However, if you only have 1 port group in the network pool ... you ONLY get 1 network (org or vapp) not both.
In almost every case I have seen, they don't use a Port Group Backed pool .... VXLAN or vCNI are the more common options. mostly since a single vLAN = 1000+ networks.
If you wanted a network to go to the "outside world" delete your network pool (unlink from the org vdc after all are deleted), create an external network in system (using the port group) ... make an external network in the organization linked to the one in system. then putting a VM on that network will put it directly into the outside network.
having a network pool could make an additional layer. like having a local network with a gateway to the outside world.