To do some basic testing of vCD you need to have a network pool, external network, and organizational network setup. A basic setup would look like this:
Setup the network pool as Network-Isolation backed. You must have 2 different VLAN's configured on the switch your NIC's connect to. Only one will be setup within your dvSwitch and the other will be used here. I personally think this is easier than the other two methods though.
Then create an External Network which will connect to your dvSwitch Port Group you created. Give it some IP's not in use and not in a DHCP scope.
No you'll create your Org Network by selecting "Connect directly to an external network"
When you create your vApp you'll have to add a network to it. This network will be your Org Network. Make sure the nic also is set for "IP Pool" for it's IP address.
Eric