You can select from several operating systems when creating a VM:
You can also upload your own ISO and qcow2 images to the panel and provision VMs from the images.
To upload an image, go to Images, and press Add a New Image.
Then, to provision a VM from the image, select the image under My Images when creating a new VM.
For ISO installation images, you'll need to complete installation over VNC, and then press Swap Boot Order to boot to the local disk.