In a very simple way when a page uses https (its address starts with this acronym instead of http) what it is doing is using a more secure form of communication for sending data.
When a web page asks you to enter a data such as a phone number or password and offers you a button that says SEND when you press it, what you are doing is sending that information to a computer somewhere in the world . Now imagine that this information was in an envelope that transports a carrier pigeon, what would happen if in the journey of the pigeon a person catches it and opens the envelope? Well, it would simply intercept the communication and see what you are trying to send. In addition, you can then return the pigeon to your route without you having heard anything.
When you use HTTPS, that communication is encrypted in such a way that if, by following the example, someone catches the pigeon and opens the envelope, it will not understand what is going on or it will have to be deciphered in some way.
This is why many Internet banking and shopping sites have addresses that start with HTTPS because they use this system to protect the information that is sent through their pages.
Over time it has been shown that HTTPS is not only necessary for banking data, but its use is highly recommended in messaging services such as Facebook or Tuenti and in email sites such as Gmail or Hotmail. In some of these sites it is up to you to activate it or not and in others it is activated by default.
Our recommendation is that whenever possible you activate it since the page will work exactly the same and you will be safer using it. However, a page using HTTPS does not mean you do not have to worry about anything else, you have to add things like a good choice of passwords or the installation of antivirus on your computer.