Inside section 11 (Progressing from stage1 to stage2), at the end of the second paragraph there is a link to read up on USE flags; this link points at "http://www.gentoo.org/doc/use-howto.html", which does not exist. It should point to "http://www.gentoo.org/doc/en/use-howto.xml".
Please be patient. D.Robbins are changing the docs layout in the moment to be more i18n frendly. This is still in progress, so some of the links are still broken.