What is the difference between NIS(Network Information System) and NFS(Network File System)

NIS is designed to share out information in specific files (e.g. passwd, group, hosts) so you don't have to setup the entries on each individual server.
A good example is passwd where you typically have users in /etc/passwd on local host and would have to do the useradd of each user on every server. By using NIS to create a passwd map and share it out from one NIS master you can quickly have a new user available on all hosts.

NFS on the other hand is designed to share out entire filesystems rather than specific files. A common use for this is to share /home from one server to all your other servers to save space. Every user has the same home directory on each host so you don't tie up space from each host.

If you use NIS to share out passwd and group and NFS to share out /home you can have a central server that contains all the information for your users.

Of course you wouldn't want to do this for key system accounts such as root or for the root filesystem. Also as may be obvious the downside to using NIS/NFS is that if the central server goes down then all your users on other hosts no longer function. NIS allows for slave servers to mitigate this but NFS doesn't.

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Looking at this--and your previous thread--it seems more likely that you are posting a homework question. In the first thread, you have a reply which includes a link on how to setup NIS. I have a hunch that that link should help answer your question