Basically, the Hypertext Transfer Protocol (HTTP) is the language by which the web client (usually the browser) and the Web Server “understand” each other.
Since the lack of encryption in the HTTP transmission protocol facilitates criminal activity and metadata espionage, the Hypertext Transfer Protocole Secure (HTTPS) was developed. This version of HTTP operates in encrypted transmission.
The aim is, on one hand, to prevent an unauthorized third party from “eavesdropping” on the communication (e.g. it could become aware of WLAN network traffic). On the other hand, the Web server is authenticated by the fact that at the very beginning of the communication, a certificate (called SSL certificate) is sent to the web client to attest the credibility of the domain on the server: this measure helps combat deception resulting from fake websites.