In plain English
HTTP describes how a client asks a server for something and how the server responds. It supports loading web pages and exchanging data through APIs. Responses include a status code indicating what happened. HTTPS uses HTTP over an encrypted connection to protect the exchange in transit.
Example
When you open a startup's dashboard, your browser sends an HTTP request for the page. The server replies with a status code and page content. Using HTTPS encrypts that exchange in transit.