Field
Subject: Each viewpoint article is assigned subject tags. For example, an article on abortion might be tagged with the subject reproductive rights and so might an article on birth control. So using "reproductive rights" as your term and setting the field to Subject will pull in all articles that are tagged with the "reproductive rights" subject tag.
Document Title: If you want a specific word to appear in the titles of your results, set the field to Document Title. For example, if you want to see articles where "climate change" is in the article's title, type climate change in the terms box and set the field to Document Title. Your results will be resources where the words "climate change" appear in the resource's title.
Entire Document: To increase the number of results, try setting the field to Entire Document. The search will scan entire documents for your keyword and will pull any article/resource where your keyword is found.