In the olden days, when creating an index for a book, you'd read each page of the manuscript. Each time you encountered a term or an idea that you wanted to appear in the index, you'd write it down along with the page number. When this process was finished, you'd painstakingly re-sort your list into alphabetical order.
Life is too short.
Today, many indexes are prepared by software, which generates an index automatically from your word-processing file. This system creates index entries only when the actual indexed word appears in the text. If you, like many book authors, are charged for indexing by your publisher, volunteer to do the index yourself. And their indexes aren't always very good. With EZIndex, I can create my own absolutely terrific indexes myself in an incredibly short time.