Keyword searching is how you typically search web search engines (ex. Google). Think of important words or phrases and type them into the search fields to get results.
When you search by keyword you are searching for words and phrases that can be found anywhere in the text of the article.
Subject headings describe the content of each item in a database. Use these headings to find relevant items on the same topic. Searching by subject headings is the most precise way to search article databases.
To find subject headings for your topic:
A general database covering many areas of academic study. Find articles from over 7,000 full-text periodicals and abstracts from more than 11,000 additional journals.