To log in to Square, start by navigating to the Square website or opening the Square app on your device. Enter your registered email address and password into the respective fields. If you have two-factor authentication enabled, you will be prompted to enter the code sent to your mobile device or email. After entering the correct credentials, click "Sign In" or "Log In" to access your Square account. If you encounter any issues, ensure your email and password are correct or use the "Forgot password?" link to reset your login details. For additional security, consider using a strong, unique password.