To create a bootable CD-ROM/DVD, burn the ISO image netboot.xyz.iso to a blank CD-ROM/DVD. Insert the media into the server, set the proper boot order and boot up.
You can also use these ISOs to boot any sort of VM in Citrix XenServer, VMware ESXi, VMware Fusion, VirtualBox.
They are great for attaching to remote virtual media of a server like the Dell DRAC or HP iLOs. Because the iPXE boot disk is so light weight, they are great for starting installations where there might be really low bandwidth.