Here, you explain a little more about surfaces. Good. :) Please explain why I can have several surfaces - and: are those stacked? Is there a z-axis? Are they like layers in Gimp/Photoshop?
Something like "Imagine the surfaces as a range of layers or screen you draw your items on. They can be stacked, rearranged or work like non-destructive layers work in Photoshop: You add an effect on one surface and overlay some other surface with it. Surfaces can be duplicated (copied? cloned?) and reused" and so on.. (I just made that up by assuming that this is how surfaces work in SDL, please ignore it if I'm plain wrong here and explain how they really work. :)
In the "coordinates" paragraphs you refer to the documentation. I would add at least three sentences here on the subject of blitting (another jargon thing you either know and understand or you're totally lost wtf blitting might be. ;) Explain it and explain what blitting's got to do with coordinates (overlapping? intersections? unions? What does blitting actually do?)
A little later this code example pops up:
List the three most important draw_something by their real names. (Didn't you mention at the top of the chapter that you can draw primitives, images and text? Are those the somethings? If not - how do I get from those three to the draw_somethings? Are they related somehow?)
Why would I need to know the pixels at this point? What's it good for to be able to address every single pixel of my surface? What's a common use for it?
Now more details about surfaces are coming up - don't spread information this way, it makes it hard to follow.
Also: Are Images surfaces? Or do I put an image onto a surface? Or do I create a real surface type like "an image surface"? Do I have to stick with it? Can I change it?
What libary is it I would need for the mentioned image support? Name it.
Is Video "video" as in "mpeg avi moving images"? :)
Oh, and why do I have to know about Image and Video, if generally the Sprite module is used? Why? Are those sprites like in web programming? What's a sprite in game jargon?
"Sprites add several features" - which one? Name a couple and add a short explanation why those are useful/helpful/mandatory/good style/plain stupid if not used...