The very first part of the URL indicates exactly how the resource should be accessed. As a user, you usually don’t have to worry about this, but the programs on your computer do. Web pages use HyperText Transfer Protocol (http://) or encrypted HyperText Transfer Protocol Secure (https://) to transmit information, which is why the URLs of web pages begin with http:// or https://
What’s important for Search Engines?
In April 2004, Google talked about using HTTPS as a ranking signal and the Noisy Little Monkey view on this is that, yeah, it probably gives a small boost to your rankings but at the time of writing, unless you’re planning to make the jump to https anyway, there’s a bunch of other stuff you can do to give Google the right signals.
What’s important for everyone else?
Collecting credit card details on your website? Then it stands to reason that you’ll need https to provide security and earn the trust of your purchaser. The issue becomes a bit muddy when we think about collecting names and addresses via contact forms… Someone wants you to call them so they can find out more about your service. Do you need https to transfer that data securely? The short answer is “yes, probably” but it can be expensive and confusing for the layman.
If you’re concerned that you’re not taking “appropriate measures” for an organisation of your size, you should check out the ICO’s information for organisations: https://ico.org.uk/for-organisations/
There are other types of internet traffic which use different protocols. For example when you want to upload or edit a file to your website without resorting to a CMS (Content Management System, like WordPress), you are directly addressing files on a web server. This is typically done via File Transfer Protocol (ftp://) or SSH File Transfer Protocol (sftp://). As a consequence, applications which use this protocol use URLs which begin with ftp:// or sftp://