I have two articles, A and B. I would like to display them like this:

AAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAA
AAAAAAAA BBBBBBBBBBBBBB
AAAAAAAA BBBBBBBBBBBBBB
AAAAAAAA BBBBBBBBBBBBBB

(i.e. the B article is in the bottom-right corner of the page).

I looked up some CSS manuals, but all manuals I found just explain how to put B in the top-right or top-left corner, or in the middle-right or middle-left part of the page (by using float). Do you have any idea how I can do this?

(if I put the div that contains B after the div that contains A, and then make B float, it is printed after A and not inside A as I want).

It sounds like you are looking for page-layout functionality similar to that found in desktop publishing systems like Quark or Adobe InDesign, in which the page is divided into regions and content flows into them.

The CSS model doesn't quite work like that, although there have been proposals to extend it in that direction. To achieve what you are trying to do in CSS will require placing article B within article A, in the location at which you want it to float next to, such as between two paragraphs. Some tweaking of the content may be necessary to get the positioning that you would like.