If news search results are particularly relevant for your search, they will appear automatically. (e.g. weekend box office)
For some searches, news search results are particularly relevant, but are not the best instant answer for that search. In those cases, you can get news search results by clicking News under the search box. (e.g. philadelphia)
If you add the word news to your search, news search results will appear automatically no matter the search. (e.g. cat news)
To expand the news search results, click the grid icon at the top right of the news search results. To then collapse the results, click the X icon at the top right of the results.
You can also use bangs to search for news using other websites right from the DuckDuckGo search box. There are bangs for The New York Times (!nyt), The Wall Street Journal (!wsj), and CNN (!cnn). For example, !cnn politics would search for politics on CNN. The full list of bangs are on the bang page.