gnus gnub question

[notbob]

I'm still a novice emacs user, but am learning.  Now trying gnus for
usenet after using slrn for yrs.  Not too hard, as many gnus key commands
are the same as slrn.  I've have one problem and a couple questions.

According to O'Reilly's Learning Gnu Emacs, DEL is the key to scroll
an article backwards.  It doesn't work for me.  I get this in the
mini-buffer:

Buffer is read-only: #<buffer *Summary gnu.emacs.gnus*>

I'm running emacs 22.2.1.  Is there a different scroll back key, now?

The questions are, when I catch-up a group and then re-enter,
specifying n number of articles to bring up, all the articles are
colored cyan and have an O to the left of the article.  What does this
mean?  Also, in summary buffer, what do article titles bracketed with
greater/lesser brackets mean ( < subject > )?

I hope this posts.  ;)

nb