Whoa, slow down.
What are you trying to port forward for?
For a SIMPLE example lets say you want to host a WEB server which uses port 80 tcp, and that's it.
Your whatsmyip is what the public sees so forwarding to there is just making a redundant statement, forget that. They already know that IP or you will give them that IP.
Your PRIVATE computer IP you choose to do the web hosting lets say its 192.168.1.2 [command prompt ipconfig to figure out what it actually is at that computer] so your port forward config would be port 80, tcp, 192.168.1.2
then any connection to the watsmyip on port 80 would be forwarded to your specified server at 192.168.1.2 and it would respond correctly.
There are two port types tcp and udp, you just need to know what the app in question uses, if you want to learn more, google is your friend.