Security - the big difference between HTTP and HTTPS
Regular HTTP connections are fundamentally insecure. Any data sent back and forth between your browser and a web server is vulnerable to be intercepted or tampered with at any point along the connection.
By contrast, secure connections using HTTPS are encrypted end-to-end. Any potential Intruders will be unable to see the communications – particularly important whenever transmitting sensitive data, such as passwords or credit card details.
Chrome security indicators (From top to bottom: HTTPS, HTTP, broken HTTPS).
Ensuring you get the experience you expect
HTTP web traffic is vulnerable to attackers modifying or tampering with web content. This could be done to inject advertisements or to insert fake content, or to trick the user into downloading and installing malware. Some mobile internet providers also heavily compress web data which can result in loss of image quality. HTTPS ensures that none of this can happen.
Enabling new browser features
Due to their sensitive nature, many of the web platforms powerful new features also require HTTPS. It will be required for any site that wants access to device features such as the GPS and camera. Its also needed for sites that would like to increase engagement with push notifications, or sites that want to work offline using offline storage.
Giving sites a search boost
Since 2014, HTTPS has also been used as a signal in Google’s search ranking algorithms, giving site owners a strong incentive to upgrade to a secure connection. Eventually web browsers will display a stronger warning that regular HTTP connections are insecure. (via Google Security blog)
If you want to turn on secure browsing, you'll need to go into the Privacy settings on your internet browser of choice (Google Chrome, Safari, Internet Explorer etc.) and turn it on. A quick online search will give you the exact route to do this, as well as some other tips for keeping your informations secure online.
All you really need to remember is summed up in this tweet from Google Chrome's online security guru Adrienne Porter Felt.