Normally you just do "COMMAND+K" to bring up the "Connect to server" dialog, or use the Go menu in Finder. Then it's 'protocol://<address>/<share name>
Example:
nfs://192.168.1.2/share
You can use /Applications/Utilities/Netinfo manager (I think) to add the server's IP address and netinfo name so you can refer to it as
nfs://server/share_name
rather than type the IP. But you can also bookmark it and call it up each time.
Finally, there's also /etc/fstab that you can edit to have those volumes mounted on startup.