I don't have the book with me. I'll get my copy and check that page. In the meantime, maybe some definitions will help.
I understand your confusion. Leading article and intro sound like the same. And it's further complicated by featured articles and category intros. Lots of introductions to choose from. I'll try to define these for you and see if that makes it clearer.
A leading articles are simply the first ones on the page. Anytime you choose a menu item with a blog layout, you can say how many columns the articles take on the first page of the blog layout, and how many leading So you determine that at the time you you create the menu item.
Also at the time you create the menu item, you can choose the order you want the articles to show. So you can arrange them alphabetically or by creation date or some other automatic order.
You can also use the featured item check box on the article manager when you create the article itself. Clicking Featured when you create the article will make it appear first.
Intro's are a bit different. If you are trying to create an introduction to the category or section, that always stays at the top of the page, you create that when you create the category by filling in the category description.
If you want your articles to appear with teasers, instead of the full article text, you create an article intro by using the "read more" link in the editor window when you are creating the article.
Let us know if that clears it up. I'll get back to you as soon as can get to my book to check your exact reference.
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