The answers would be in your text or books. And if stuck you ask your TA or prof. What good is getting the answer if you can't explain it?
I have a course at the university which requires us to configure a simulation network with GNS3.
In this network is a pfsense firewall with a WAN interface (connected to the internet) and 2 internal subnets.
The setup also includes port forwarding from one subnet to the WAN interface. We also had to set the redirection port to 80 and the destination port to 80 on the pfsense.
The questions we got about this setup are:
Why the entry needs to set two ports, destination and redirection?
Could the two fields have different values and if so when would this be useful?
Does anyone know the answers to these questions?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic