Explanation for a noob - setting up port forwards

[MakOwner]

I have port forwards setup and working, but there are some options wiht the port forwards that I don't quite understand, and all of the material related to the options seems to be circular (to me at least) in that everything references each other assumes that the user understands the concepts described by this basic sentence.
I don't.

I have the book - I have purchased the lates iteration.

Last option on the NAT page where you set up forwards:

Filter rule association: Choose one of Add an associated filter rule gets updated when the port forward is updated, or Add an unassociated filter rule, or pass which passes all traffic that matches the entry without having a firewall rule at all.

What does this do/mean?  Any particualr place in the book I'm missing the explanation?

[KOM]

What does this do/mean?

It's talking about an associated firewall rule to go along with the NAT rule.  You need both.  The NAT rule does the mapping ad the firewall rule allows the traffic.