iptables excercises and test studies

Hello. I'm trying to fully understand iptables with a book and man but I would like to know if anyone knows about any excercises or test studies I could apply to a linux OS. Particularly, I'm planning to use it on Raspbian and Ubuntu (future and current OS respectively). Thank you in advanced.

I do not know of any exercises or test studies that you can use.
Here is a link to a TUTORIAL that I have used to learn IPTABLES.
One thing to remember is always start with a totally blocked system and then open ports that are needed.