We can create a NAT instance as follows:

1. Go to the EC2 dashboard, click on Instances from the left sidebar, and click on the Launch Instance button at the top of the page.
2. Click on Community AMIs, search for NAT, and select the latest NAT instance that's available:

3. On the Choose an Instance Type page, set Type to t2.micro and click Next: Configure Instance Details.
4. Within the Configure Instance Details page, set our custom VPC to Network, set our public subnet to Subnet, leave the option for Auto-assign Public IP as is, and click Next: Add Storage:

5. We can use the default configuration on the Add Storage page. Click Next: Add Tags.

6. Add a tag in the Add Tags page with Key set to Name and Value set to My-NAT-Instance. Click on Next: Configure Security Group. 
7. On the Configure Security Group page, select Select an existing security group, select the security group that we created in the Getting ready section, and click on Review and Launch.
8. Follow the instructions shown on the screen to complete the EC2 launch.
9. Once the launch has completed, select our instance, click on Actions, click on Networking, and click on Change Source/Dest. Check:

We should see the following pop-up screen:

10. Click on Yes, Disable on the Enable Source/Destination Check pop-up screen.

In the next section, we will create a route to this NAT instance in our main route table.