Yeah. Let me give you a quick overview.
For now, the first VM that's created is broken, so you have to create a second one. So that's the first thing you do.
Once you've created the second VM, highlight it and click "devices" at the bottom. Add two devices. One of type DISK and one of type CDROM.
You'll want to choose virtio for all your devcies if you're not using Windows in the VM.
You can then turn it on and connect via a VNC client to the port listed. (the second VM should be port 5902)
You'll use your freenas login credentials to connect to VNC
From there, it's just like any other system.