http VS https

What are they:

HTTP, or hypertext transfer protocol, is the way a Web server communicates with browsers like Internet Explorer® and Mozilla Firefox®. HTTP lets visitors view a site and send information back to the Web server.

HTTPS, hypertext transfer protocol secure, is HTTP through a secured connection. Communications through an HTTPS server are encrypted by a secure certificate known as an SSL.
(SSL is added between the layers of application http and transaction tcp) The encryption prevents third-parties from eavesdropping on communications to and from the server.

When to use http and when to use https:

If the security is a big issue for the communication between clients and the server, then use https.

If the speed and performance are the main issues, use http. Http is much maturer then https.