CINAHL is a database that focuses on nursing research. You can enter your search terms in the search boxes, or you can use the CINAHL subject headings feature. The video below explains the subject heading feature.
Discover is the library search tool that searches across databases, electronic books, and print books at the same time. This is a great place to start when you aren't sure which subject-specific database is right for you, when you are doing interdisciplinary research, or when you have finished searching subject-specific databases and want to see if you missed anything.
This tutorial explains the difference between using subject headings and keywords. Many databases have the ability to search some specialized subject headings (i.e. MeSH) in addition to a keyword search. This video can help you decide which method to use.