The HTTP protocol is used for communication between a client and server, allowing access to the world wide web and enabling users to access information on the internet. The GET method retrieves data from a server at a given path, while POST requests send data to a server to create or update resources. PUT requests update and replace target resources with a payload, making them idempotent. PATCH requests partially modify resources without replacing them, and DELETE requests delete target resources. cURL is a popular command line tool used to transfer data with URLs through protocols including HTTP, SMTP, TELNET, and more. By sending HTTP requests with cURL, users can experiment with different methods and endpoints, such as the NewsAPI for fetching top headlines or Twilio's Programmable Messaging API for sending SMS messages.