Some variables relevant for moving and selecting articles:
gnus-auto-extend-newsgroupnil. Gnus will then
fetch the article from the server and display it in the article
buffer.gnus-select-article-hooknil. If you would like each article to be saved in
the Agent as you read it, putting
gnus-agent-fetch-selected-article on this hook
will do so.gnus-mark-article-hookgnus-summary-mark-read-and-unread-as-read, and
will change the mark of almost any article you read to
gnus-read-mark. The only articles not affected by
this function are ticked, dormant, and expirable articles. If
you'd instead like to just have unread articles marked as read,
you can use gnus-summary-mark-unread-as-read
instead. It will leave marks like
gnus-low-score-mark, gnus-del-mark
(and so on) alone.