I hate to say it, but "grey matter"
Have a read of this
tutorial ...
Most of the "idiot proof" GUIs make a lot of entries that are out of order, hard to read etc.
do
iptables-save and see the final result, sorted into order. Much clearer..
I think the idea is to learn it once, the tutorial does a good job of explaining things, then write/modify/disassemble a complicated one for the exercise.