The Ubuntugeek have a guide to setting up the NFS server and Client in Ubuntu.
Read more here
NFS was developed at a time when we werent able to share our drives like we are able to today – in the Windows environment. It offers the ability to share the hard disk space of a big server with many smaller clients. Again, this is a client/server environment. While this seems like a standard service to offer, it was not always like this. In the past, clients and servers were unable to share their disk space.