HTTP
HTTP is an insecure protocol that browsers like Chrome will often flag as unsecure. Technically speaking an average computer geek can easily see exactly what you are looking at when you visit a HTTP website. Furthermore if you login or enter credit card details on a HTTP insecure website, your data can be stolen fairly easily by anyone.
HTTPS
HTTPS is a secure protocol that uses an encrypted connection, preventing anyone from seeing your online activity or stealing your data. In order to use the HTTPS protocol you must have a valid SSL certificate. This is used to establish a secure, encrypted connection between your browser and the web server.