Network Address Translation

NET is used due to insufficient number of IPv4 address for all internet connected device . 
How NAT Works 

NAT usually lives inside your Router. Here is how it handles your data:
The Request: You sit at your laptop (Private IP: 192.168.1.5) and request to see google.com.
The Translation: Your router receives this request. It knows 192.168.1.5 cannot travel on the public internet. It "translates" your private address into the router's Public IP (e.g., 203.0.113.10).
The Table: The router makes a note in its NAT Translation Table. It records which private device requested which website and through which "Port."
The Response: Google sends the data back to your Public IP. The router checks its table, sees the data is meant for your laptop, and passes it back to 192.168.1.5.

Types of NAT
There are three main ways NAT is implemented:
Static NAT: Maps one private IP to one public IP. Usually used for servers inside a network that need to be accessed from the outside.
Dynamic NAT: Maps a private IP to a public IP from a group (pool) of available public IPs.
PAT (Port Address Translation): Also known as NAT Overload. This is what you use at home! It allows thousands of devices to share one public IP by assigning each device a unique "Port Number."

The Benefits of NAT
IP Conservation: We don't need a unique public IP for every single smartphone and tablet on Earth.
Security: NAT acts as a natural firewall. Since your private IP is hidden, hackers on the internet cannot see your device directly; they only see your router's public address.
Flexibility: You can change your internal network setup (add or remove devices) without having to request new IP addresses from your ISP.