“Above the fold” means the part of a page visible before the reader scrolls. On the web there is no single fixed fold: viewport size, browser controls, zoom and text wrapping all change it.
Put orientation early
Make the page’s purpose clear near the beginning. For a reference lesson, a useful opening names the concept, explains it briefly and leads toward a working example. Avoid crowding every detail into the first screen merely to keep it visible.
Inspect actual viewports
Open the page at a narrow width and a short height. Then zoom in and increase text size. Note which content appears first and whether a reader can tell there is more below. A desktop screenshot does not establish the opening on a phone.
Exercise: compare the first screen of a lesson at two viewport sizes. Can you identify the topic and the next useful action in both? If a large decoration hides that information, simplify it or move it.
Let the page continue naturally
People can scroll. Material below the fold remains part of the document; it is not inherently hidden or unimportant. Organize longer content with headings and useful links rather than shrinking type or removing necessary explanation. See responsive design and hero sections.
Sources
Reference 1 provide the technical details and current compatibility information.