WAF stands for web application firewall. It is used to secure the application and Layer 7 traffic. WAF helps you secure your application from bad guys on the internet who always try to hijack your application and database using malicious scripts or headers.
It monitors the content delivered through CloudFront or an application load balancer, whereas the Shield service is used to protect from a DDoS attack on applications at the content delivery platform (CloudFront), DNS (Route 53) level, and load balancer (ELB).
You can enable WAF's role with AWS Application Load Balancer (ALB) or CloudFront.
To enable WAF, log in to AWS Management Console and, in the security section, select WAF & Shield. Now click on Go to AWS WAF: