Sharing a directory using NFS to other Linux systems is a common and handy way. To be able to explain briefly, let me separate tasks into two as server and client side. I use Oracle Linux 6 and Oracle Linux 5 respectively as server and client, though just the opposite goes through same steps. However these commands should run on every Red Hat based system.

On the server that you will create the share, edit the export file:

$ vi /etc/exports

Add line(s) to file such as:
/share_dir *(rw,sync,fsid=0) 

Pay attention not to use extra space on a line, it may cause a problem. Here, instead of "*" - which means sharing is for every one, to world - you can use client's IP or FQDN as shown above. Also if it's going to be read-only share write "ro" instead of "rw". We use "fsid=0" parameter not to get "mount.nfs4: Operation not permitted" error.

Permissions of directory, "/share_dir" and/or "/shares/nfs", should be read and execute to others if it's a read-only share or read-write and execute to others if it's writable. Otherwise you will face with "mount.nfs4: Permission denied" error when mounting the share. So alter permissions of directory:

$ chmod 757 /share_dir

Restart related services (If your server is Linux 5, use portmap instead of portreserve. ):

$ /etc/init.d/portreserve restart
$ /etc/init.d/nfs restart

You can check shares by:

$ showmount -e <server_ip> 
$ exportfs -avr

On the client simply mount the share by:

$ mount -t nfs4 <server_ip_or_host_name>:/ /mnt

Notice that, even the shared directory is "/share_dir" or "/shares/nfs" we use "/" only.