Trying to understand D3 and the like....

So in an attempt to understand D3, I have been working through some of the information on this page D3 for Mere Mortals.

However, I can't really make the code work.

I have had to learn a bit about SVG - scalable vector graphics.

You can use svg to create code on websites to give you boxes and the like. Clearly boxes are just a simple start but hey... Can I add code to this page to make a box here with SVG? YES!!! This seems to work. Here is a different colour box: So the coding goes as follows svg is a html tag like heading or paragraph. There are various shapes, colours, lines and the like.
Looking at the code: you have "rect" for rectangle of particular width and height. You have fill, stroke, stroke-width, fill opacity and the like.
I got the code from w3schools.com.