To set up an isolated Network, log into your controller and go to Settings->Networks and click on the +Create New Network button. This opens up the “Create New Network” page, where you need to provide a few details. First off, give the network a name and select Corporate as the Network Purpose. I left the default Network Group of LAN1 in place, since I don’t have anything connected to the LAN2 port of my USG.
Next up, define a VLAN ID that you want to use for this network. This can be any number from 0 to 4095, and you can pick whatever you want here (as long as it’s not 0, which is the default VLAN for everything that doesn’t have one defined).