so to break it down, that first box will be the internal address of your device (so its 192.168.0.____, fill in the blank using the method above). the ports require a bit more info, but the usual method of headless pi access is SSH on 22 and SOMETIMES telnet on port 23, so make them 22 and 22 or 23.
the external address could be for a static point to point connection, but more likely it is for your own external address, the one that your router holds on the internet, so google whats my ip and make a note. (POINT TO REMEMBER - this may and probably will change each time your router turns off/on, most IP addresses are on a DHCP style config, so if it stops working do another "whats my IP") ports need to mirror your internal ones
where it says both, the other options are probably TCP and UDP, you can read up on these in much more detail elsewhere but the odds are your going to want TCP for most of your networking, so go TCP or both. i havent seen a UDP only system in a long time.
lastly, easy one, enabled is just telling your program if this rule is active or not, so you can set up a dozen rules and have them inactive until you need them.
internal IP = 192.168.0.XXX (i would do an arp scan to find all IPs on network);
ports 22-22 or 22-23 for internal/external ports;
remote host = whats my ip result from google;
protocol TCP or both;
remember to enable!