I like the website, Giphy, because it has a lot of funny image on it, and they make me laugh. In order to make the gif possible, I believe they added a image source in order to put the gif in code.
The HTML website, W3 Schools, is a great website for learning HTML. There are demos on the website to give you examples, and a list section on what code does what. I recommend this website if you are learning html for the first time. 4 out of 5 stars.
The HTML website, Codeacademy, gives you the basics on HTML. Once you actually sign up for the website, it appears to be somewhat like Khan Academy, where you can personalize your own learning experience based on the lessons you choose. The only thing that bugs me is that you have to sign up for the website before you can do any lessons, and that there are lessons you have to unlock by doing other lessons. 3.5 out 5 stars.