The planning and configuration of Network Address Translation/Port Address Translation is similar for security device as a router.
Define your internal IP address space to translate. This will help with choosing the right network translation scheme for your application. You will configure an access list in order to define the ip address to be translated.
Define your inside and outside interfaces. Make sure you have configured IP addresses for these interfaces.
Map out your ports! This will be helpful for the firewall policies that will need to be built later.