Using search fields effectively is an important step towards becoming an efficient searcher.
Often the default search field will be something like "all fields" or "search everything." This search field will retrieve lots of results as it's looking for your keywords in any and every part of the article (title, abstract, full text, metadata, etc.).
You can, however, choose more focused options. We'll provide screenshots with examples from a few databases.
PubMed: In this case I'm searching for "DASH Diet" in either the title or abstract of the article, and for "hypertension" as a MeSH Major Topic.
Scopus: Here we've used Scopus' TITLE-ABS-KEY field along with their AUTHOR-NAME field.
Most databases have a "help" document of some sort - this is a good place to learn more about their search field options.