The initial steps are easy but the remaining steps depend upon what you want NIS to do. Manage usernames, groups, automount maps, services, hosts, ...
1) edit /etc/rc.config.d/namesvrs
and set NIS_CLIENT=1
and NIS_DOMAIN="acme" (or whatever your domain is)
2) /sbin/init.d/nis.client start
Now you must alter /etc/passwd, /etc/nsswitch.conf, /etc/groups, automount maps, ... depending upon your needs.
If it ain't broke, I can fix that.