This is definitely my favorite! Jonathan talks mostly about PHP forms in this part, and how to use them to change your webpage. Like once, he made it so you can have a color form:
And when you select a color and press the submit button it will use that color for the background of your page. Just love it! And using this, I was able to create a form that let's you choose the background, size, and placement of a color <div> tag. The code for the above color form is:
It won't do anything, of course. Just watch the video to learn all about forms and inputs!