Can someone explain to me how to port forward?

so i have a question about port forwarding, i want to forward the following ports for steam
https://support.steampowered.com/kb_article.php?ref=8571-GLVN-8711
because i have been having some issues
Now my question is when i enter my routers setup page the table for forwarding ports i see internal and external, now whats bugging me is that i don't know whether to put the ports in internal or external?
Could someone help me? Here's the print screen of how the layout looks, and the ports i need to forward are in the link.

 

Also, when i was looking at the guide, the picture of the table to fill up is difrent
Mine has internal-external parts and that one does not.
Mine has 2x Start port and 2x End port and the one on the guide does not?
Its for the same router.
Why is my difrent?