Consult the documentation for your PXE card to configure the host to boot via PXE.
When the diskless client boots, it mounts the remote root/ directory in the diskless directory as read-only. It also mounts its individual snapshot directory as read/write. Then it mounts all the files and directories in the files and files.custom files using the mount -o bind over the read-only diskless directory to allow applications to write to the root directory of the diskless environment if they need to.