The sign-up or login process with OTP created using PHP and PHP Mailer is a secure authentication method. Users register with their details, and PHP generates a random OTP associated with their email. The OTP is sent via email using PHP Mailer. Upon receiving the OTP, users enter it on the login page. PHP validates the OTP and grants access if it matches. This process enhances security, protects against brute force attacks, and offers user convenience. By leveraging PHP Mailer, OTPs are seamlessly delivered via email, ensuring reliable and authorized access to the system.