The following commands are available in the Gnus summary buffer:

SPC

If there is no article selected, select the article on the current line and display its article buffer. Otherwise, try scrolling the selected article buffer in its window; on reaching the end of the buffer, select the next unread article (gnus-summary-next-page). Thus, you can read through all articles by repeatedly typing SPC.

DEL

Scroll the text of the article backwards (gnus-summary-prev-page).

n

Select the next unread article (gnus-summary-next-unread-article).

p

Select the previous unread article (gnus-summary-prev-unread-article).

s

Do an incremental search on the selected article buffer (gnus-summary-isearch-article), as if you switched to the buffer and typed C-s (Incremental Search).

M-s M-s regexp RET

Search forward for articles containing a match for regexp (gnus-summary-search-article-forward).

M-r regexp RET

Search back for articles containing a match for regexp (gnus-summary-search-article-backward).

q

Exit the summary buffer and return to the group buffer (gnus-summary-exit).