Before you begin searching for information, you should understand the topic you are researching. Dictionaries and encyclopedias are a good place to begin. Dictionaries provide definitions of unfamiliar terms, whilst encyclopedias give more detailed explanation and overview of topics.
Dorland's Illustrated Medical Dictionary by 
Encyclopedia of Family Health by The Oxford English Dictionary is an unsurpassed guide to the meaning, history, and pronunciation of over half a million words, both present and past.
Need a definition; an explanation; a map; an illustration; a quotation? Try the Oxford Reference Online ... it's got them all!