We haven't talked about the "S" part of the HTTP equation yet. Specifically, the S stands for security, unlike Superman's, which apparently isn't an S, and is actually the crest of the House of El.
Unlike Superman, web servers could be lying to you.
When you visit a website, you like to know that the website you're hitting is legitimately owned and operated by the company you believe it to be. If you go to Amazon, Apple, or PayPal, you want to know that they are who they say they are before you hand over your digital cash.
However, you also want the website to be able to take your credit card information in a secure fashion so that those digits and secrets don't get spread over the internet in plain text format for anyone to read.
Look out for the padlock:
Most browsers (if not all) should show a little padlock when...