Unlike using Google, library research relies heavily on the use of "keywords" - the words that you will enter into a search box to begin your research. Since one author may use different words than another to discuss the same topic, you will want to brainstorm synonyms for important words, and conduct multiple searches.
For a topic like food, then, you might want to use synonyms like nourishment, sustenance, meals, or cooking. You might also conduct multiple searches, such as:
- "Vikings food"
- "Vikings nourishment"
- "Vikings sustenance"
Using keywords in this manner will help you find additional sources that one search alone might not reveal.