After configuring a tftp server, you need to set up a DHCP service on the same host machine. Refer to the Red Hat Enterprise Linux 6 Deployment Guide for instructions on how to set up a DHCP server. In addition, you should enable PXE booting on the DHCP server; to do this, add the following configuration to /etc/dhcp/dhcp.conf:

allow booting;
allow bootp;
class "pxeclients" {
   match if substring(option vendor-class-identifier, 0, 9) = "PXEClient";
   next-server server-ip;
   filename "pxelinux.0";
}

Replace server-ip with the IP address of the host machine on which the tftp and DHCP services reside. Now that tftp and DHCP are configured, all that remains is to configure NFS and the exported file system; refer to Section 24.3, “Configuring an Exported File System for Diskless Clients” for instructions.