No, don't start at http://www.w3schools.com/. w3schools.com is the worst resource for web design and development on the net. Half the information there is either out of date, incomplete, or just plain wrong.
That is total and utter BS. After thorough scrutiny by a whole bunch of coding nerds of the whole site, which consists of many hundreds of pages and even many, many more topics, the nerds found a couple of matters that were not 100% correct. Well, that is quite normal, isn't it? You will find those in any such an extensive website.
And next to that there is little wrong with its content, w3school is by far the best site from a didactic point of view. And I mean: by far by far!
Just try it for yourself, Desopno, and see that that treehouse project is not even worth tying the shoe laces of w3schools.
How to: Target IE in, Position in, Center in, Create a Fixed ('Sticky') Footer with, and Create a Drop-Down/Fly-Out Menu with CSS: Website Laten Maken Amsterdam