To sign in to Zearn, visit the official website or open the app. Click on the "Sign In" button located on the homepage. Enter your registered email address and password. If you don’t have an account, click on "Sign Up" to create one. For password recovery, use the "Forgot Password" link. Once logged in, you can access the personalized math lessons, assignments, and progress tracking tools offered by Zearn to enhance your learning experience.