This is the news page. It lists all of the news items on your site. The Legumeinfo Jekyll theme does not provide a news page since not every site may want such a page, but a news layout is provided so sites that want a news page don't necessarily have to implement one from scratch.
The items listed on this page are Jekyll posts. When the site is built a separate page is generated for each post. A news item layout is provided by the Legumeinfo Jekyll theme for these generated pages.
The news card on the right side of this page is not actually specific to this page. The Legumeinfo Jekyll theme supports adding this card to any page via YAML front matter.