When something needs looking up, reference books are useful. Here are some tips to help when using reference books.
An Atlas is a book of maps, so can be used for looking up places and place names.
Biographical index is information about people famous in a particular industry.
Dictionaries are used for looking up spellings, pronunciations and meanings of words.
Directories are the names and addresses of people and businesses or organisations, usually arranged in alphabetical order.
An encyclopaedia has information on lots of different subjects, again, usually arranged in alphabetical order for ease of reference.
Guidebooks often contain information useful for travellers to different countries or cities.
A manual or handbook gives instructions for how to do or use something (such as a kitchen appliance).
A thesaurus is similar to a dictionary, but instead of meanings of words, contains a list of words that mean the same thing (synonyms).