Go into the "NETWORK" part of the user interface, then "GLOBAL CONFIGURATION", and look for "IPv4 Default Gateway". The IP address in there should be the IP address of your router. If you don't know what the IP address of your router is, you can google "how do I find out what my router's IP address is" for your appropriate operating system (Windows? whatever).
If *THAT* still does not work, please let us see the output of "ifconfig" in your FreeNAS shell, post it here.