A Network Address Translation (NAT) gateway in Amazon Web Services (AWS) is a highly available, managed network component that enables instances in a private subnet to connect to the internet or other AWS services, but prevents the internet from initiating connections with those instances. NAT gateways are used to provide outbound-only internet connectivity for instances in private subnets, which do not have public IP addresses or Elastic IP addresses. 

There are two types of NAT gateways: 

1. A NAT gateway using a public IP address: This type of NAT gateway allows instances in your private subnets to connect to the internet or other AWS services, but does not allow incoming traffic from the internet to reach your instances. The NAT gateway uses a public IP address to connect to the internet, and the traffic from your private instances is translated to the NAT gateway's public IP address before being sent out to the internet. 
2. A NAT gateway using an Elastic IP address: This type of NAT gateway works in the same way as a NAT gateway using a public IP address, but the NAT gateway uses an Elastic IP address instead of a public IP address. An Elastic IP address is a static, public IP address that you can assign to your NAT gateway and that you can use to connect to the internet. 

To use a NAT gateway, you will need to create a NAT gateway in your VPC and then configure your routing tables to route traffic from your private subnets to the NAT gateway. You will also need to ensure that your security groups and network ACLs are configured to allow traffic to flow through the NAT gateway. 

Creating a NAT gateway: 

To create a Network Address Translation (NAT) gateway in Amazon Web Services (AWS), you can follow these steps: 

1. Sign in to the AWS Management Console and navigate to the Amazon VPC dashboard. 
2. Look into the left-hand menu and click the "NAT Gateways" link. 3. To start the creation process click the "Create NAT Gateway" button. 4. Select the VPC and subnet in which you want to create the NAT gateway.
5. Select an Elastic IP address for the NAT gateway, or choose to allocate a new one. 
6. Click the "Create NAT Gateway" button to create the NAT gateway. 7. Once the NAT gateway has been created, you will need to update your routing tables to route traffic from your private subnets to the NAT gateway. To do this, click the "Route Tables" link in the left-hand menu and then select the route table for your private subnet. 
8. Click the "Edit" button and then add a route to the NAT gateway in the "Destination" and "Target" fields. 
9. Click the "Save" button to apply the changes to your routing table. 

By following these steps, you can create a NAT gateway in your VPC and configure it to allow outbound-only internet connectivity for your private subnets. You can also update your routing tables to route traffic from your private subnets to the NAT gateway, which will enable your instances to connect to the internet or other AWS services. 

NAT gateways are useful for providing outbound-only internet connectivity for instances in private subnets while maintaining control over inbound traffic. They can help you to secure your resources and meet compliance requirements, while also providing the connectivity needed to access the internet or other AWS services.