When I'm opening ports on my firewall what do I put in the "Private IP" area?
Do you mean port forwarding on your router? You put in the IP address of the computer you are forwarding the port to.
Just to elaborate a bit more, you should have at least two IP address. One is your WAN IP which is assigned to your router... This is the IP address you are recognized by on the Internet. The 'Private IP' you are talking about is an IP address assigned by your router which is only used to identify computers on your local network. 'The Internet' doesn't really know anything about your private IPs... Just your computers and the router. When you forward a port, the router needs to know what computer to send that data too. This is why you have to specify a private IP.
So basically your computer might have an IP of 192.168.1.60 (example), but your router might have an IP of 18.104.22.168 (example). You would use the 192.xxx.xxx.xxx address as your private IP.