NAT is basically developed to compensate insufficient number of IPv4 addresses. In this idea, each device connected to the Internet does not have their own IP addresses. Instead, router has a unique IP address used to connect to the Internet. For example, assume we have three devices and all of them want to connect to the Internet. Say private IP addresses of them are 192.168.4.2, 192.168.4.3, and 192.168.4.4. When any of them wants to connect the Internet, it uses IP address of the router. By doing so, instead of having separate IP addresses for each of the device, we use one specific IP address for the devices to connect to the Internet. Helpful Video