Suppose you want to learn about the circus. You look up circus in the encyclopedia. You may find only a few pages of words and pictures.
Encyclopedias have only enough room to include a certain amount of information about each subject.
Where to Find It Library books can give you more information about a subject. Find the card catalog on a computer or in file drawers. The drawers are filled with cards, all in alphabetical order. You'll find one card for every book the library has about the circus. You should be able to find the same information.