NAT and PAT was really a difficult topic for me to comprehend for both the CISSP exam and for my job.
The only way I truly understood it was by configuring it, and seeing the packets.
The below video is a real life demonstration of how PAT operates in the real world.
Additionally, I wrote a series of posts on NAT:
Out of the different types of NAT, I demonstrate how PAT works in the video above, I hope it helps you in your CISSP studies.