Hello Ayong
The address 192.168.2.200 is the IP address used on the outside interface for communication with the inside host of 192.168.1.1. It doesn’t have to be configured in any other place to function for NAT translation. Take a look at the diagram of the lesson:
The “ip nat inside source static” NAT configuration will cause the Gi0/2 interface of R1 to receive and accept any packet with a destination address of 192.168.2.200, and will translate the address appropriately. The outside IP address for NAT does not have to be the same as the configured IP address on the outside interface. It can actually be anything. But, in order for it to work, the outside IP NAT address must be reachable, that is, routing to reach that particular address must be in place. For this reason, it is most often the case that the outside IP address in the NAT command be within the same subnet as the actual configured IP address. In this case, we have 192.168.2.200 which is within the 192.168.2.0/24 subnet that corresponds to the Gi0/2 interface of R1.
I hope this has been helpful!
Laz