Two-factor authentication is a security process that requires two different authentication factors to verify a user's identity. This tutorial will guide you through implementing 2FA for web applications using the Vonage Verify API and Koa.js framework. To complete this tutorial, you'll need a basic understanding of JavaScript, Node.js, and a Vonage API account. You'll also set up a virtual phone number to send verification codes via SMS. The tutorial covers creating a login page, handling user inputs, triggering verification codes, checking verification codes, and canceling verifications. It emphasizes the importance of error handling and suggests implementing frontend validation and using additional APIs for more robust security measures.