We find indexes in lots of different paper information sources. Examples are non-fiction books, encyclopaedias, atlases and collections of journals. The purpose of an index is to enable you to retrieve the information you want quickly and easily.
An index is an alphabetical list of the topics contained in a printed source. For each topic the index gives a reference or references to show where in the source information on that topic may be found.
Choose a non-fiction book and find its index. Is it at the back?
Keep it beside you to refer to as you look at the following sections.