Protocols are agreed forms of communication. Computer networks require protocols to transfer different types of data reliably and efficiently – and sometimes securely – most protocols are inherently insecure.
File Transfer Protocol (FTP)
FTP is for transferring files over a network. Such as uploading files to a web server.
Hypertext Transfer Protocol (HTTP)
HTTP is for transferring web pages and their contents from a webserver to your internet browser (such as Chrome). It transfers HTML, CSS, JPG, PNG, MP3, etc, to your browser. Sometimes things like video would use a different type of protocol to play in your browser.
Hypertext Transfer Protocol Secure (HTTPS)
HTTPS is the secure version of HTTP. It is used to transfer sensitive data between a webserver and your browser. Data such as personal details, credit card details, and passwords. The data is encrypted so if it is intercepted between your computer and the webserver it cannot be easily read.
Simple Mail Transfer Protocol (SMTP)
SMTP transfers emails between your email software and email servers. You may use Gmail via HTTPS, but Gmail will use SMTP to send to another email provider.