This page explains three different search strategies for finding articles of particular methodologies. In reality, you're going to combine these strategies to be as efficient and effective as possible.
Keywords are words or phrases that you use to describe your research topic - both the content (eg diabetes) and the research methodology (eg quantitative). You can use as many or as few keywords as you like, and you don't have to include a method, although it may help narrow down your search resullts.
Databases are here to help, and their tools are designed to do a lot of the work: narrowing down your results list to the most relevant articles. Save yourself time by using limiting options like these:
You can go to Show More underneath the Publication Date slider in order to see all the options. Choices like Language or Journal Subset can limit the results to nursing journals, which can save you some time as you start to go through your search results.
While keywords are search terms that you develop, subject terms are search terms that have already been developed - each article is already tagged with subjects terms that describe it. You can copy these terms into your search to use them as keywords, or you can go to CINAHL Headings and do a structured subject term search.
Please note: If you're stuck, or just curious, consider contacting your librarian!