google 'what's my IP'
Now for the very good or bad news, if you have a static IP from your ISP, that is all you need.
If you do not have a static IP, then at some point that will change (frequently or not, randomly or not), then you will need to set up dynamic DNS, which is way beyond the scope of the the Freenas forum. If you need to do that then try googling for 'dynamic DNS teamspeak' and look into services such as NoIP, FreeDNS, or DYNDNS.