Dictionaries help to clarify terminology by providing definitions of terms. These can also be a good source of potential keywords for searches in the catalog or databases.
Encyclopedias provide background information on key concepts, theories and measures to help you better understand the field. Encyclopedia articles typically provide references to further readings where you can find additional detailed information on your topic.
Handbooks are quick sources of facts and can supplement encyclopedia articles by providing detailed summaries of broad topics in the field.