How do TLS/SSL certificates work?
TLS/SSL certificates establish an encrypted connection between a website/server and a browser with what's known as an "SSL handshake." For visitors to your website, the process is invisible—and instantaneous.
For every new session a user begins on your website, their browser and your server exchange and validate each other's TLS/SSL certificates.
Your server shares its public key with the browser, which the browser then uses to create and encrypt a pre-master key. This is called the key exchange.
The server decrypts the pre-master key with its private key, establishing a secure, encrypted connection used for the duration of the session.
Why is my website showing a "Not Secure" message in the browser address bar?
Any website without a secure TLS/SSL certificate will show a "Not Secure" message in the browser address bar. The only way to fix a "Not Secure" message on your website is by installing a TLS/SSL certificate. You can do that by purchasing a certificate from DigiCert and following the installation steps in CertCentral.