Each index works differently. Look for online help screens to learn the index's search rules. Some indexes (MEDLINE, PsycINFO) have subject headings with thesauruses and may provide mapping to lead you to the correct terms to describe your topic. Other indexes (Web of Science) require keyword searching.
For keyword searching, think about synonyms, plurals, and various conjugations; learn how to truncate to look for root words with multiple suffixes and to combine terms with operators like AND, OR, and NOT.
Many indexes provide links to the articles. Look for links labled "Article Linker" or "Get Full Text." These will show you options for linking to the article or requesting a copy through Dartmouth's DartDoc service.