The security labs are documentation and code in the format of hands-on labs to help you learn, measure, and build using architectural best practices. The labs are categorized into levels, where 100 is introductory, 200/300 is intermediate and 400 is advanced. Quests are designed to collate a group of relevant labs and other resources together into a common theme for you to follow and learn.
For more information about security on AWS visit AWS Security and read the AWS Well-Architected Security whitepaper or online https://wa.aws.amazon.com/. Also check out https://awssecworkshops.com/ for hands-on workshops, AWS Training and Certification Learning Library for official security training options.