The two pages This Week's Events and Next Week's Events list both seminars and conferences during a specified week. For seminars, this is built-in, based on their entry in gcal. For conferences, it's best to announce it via a news item in gcal (by tagging it with #news), and to also tag the announcement with the hashtag #dir corresponding to the conference folder /www/apache/events/conferences/dir. Then it will appear in the above two pages on the appropriate dates.
For example, the menu item Graduate Student Conference in Algebra, Geometry, and Topology under Events > Conferences corresponds to the folder /www/apache/events/conferences/gscagt, so the announcement for this event should be tagged #news and #gscagt (for more information click Toolbox > Adding News Items). The announcement then appears on these two pages on the appropriate dates.