how can I attach a local physical optical disc unit on my xcp-ng server to my new xen orchestra virtual machine?

Question

This is a simple situation, I have a CD/DVD of "-X-" OS and I have a small XCP-NG server with Xen Orchestra installed. I want to enter the web interface of Xen orchestra, create the new virtual machine and install it the said "-X-" OS. How do I attach the dvd unit to the virtual machine through the xen orchestra interface to create that new machine?

I've been looking for the documentation and it seems that the feature is there but I don't understand how to do it, or the explicit explanation.