When you are browsing CINAHL Subject Headings, you can add subject headings to your search by clicking on the checkbox on the left. This will pop your search terms into a box on the right:
You'll see an optional checkbox to "explode" the search term. This means that the database will search for your subject heading, but it will also search for any sub-headings underneath that term. This will expand your search results. In general, it is recommended to explode your search.
The "major concept" checkbox, on the other hand, will limit your results just to articles where the subject heading has been designated as a major concept. This will reduce your results, and unless you are working with a huge amount of search results, we recommend that you do NOT check the "major concept" box.