Identify the key words that describe your topic and use them to search the library catalog and databases. Make a list of synonyms for those words and search with those, too. Enclose words in "quotation marks" when you want multiple words to express one idea or concept.
collage and 20th century
Kurt Schwitters and collage
collage and "abstract expressionism"
Use the words AND, OR, and NOT--called boolean operators--between your keywords to broaden or narrow your search.
collage AND (assemblage OR "mixed media")
If you shorten, or truncate, a word and then use an asterisk to "stand-in" for its different endings, your search results will include multiple forms of the word.
A keyword search for Dada* will look for Dadaism and Dadaist(s).
Use Subject Terms (assigned by the Library of Congress) to find like items in the library catalog and in journal databases. If you find a useful book or article, its catalog record usually will include Subject Terms that you can use to find related research material.