Turn the pages to the back of the book that you want to use. The last section will be called the "Index". If there is a table of contents, it will list this section. Here, every topic is listed in alphabetical order.
Turn to the first letter of the topic you're looking for. Search through the words listed until you find your topic. There will be a list of page numbers next to the topic. Some will have the words "see also" after the numbers or in place of the numbers. These words will be followed by another topic related to the one you're looking for.
Look at each of the pages the index listed for your topic. The pages are listed in numerical order, so you can search through the book from front to back.
Use the index again if you weren't able to find the information you wanted during your first search. Make sure you looked at each page listed. Use the "see also" topic. Look at all of the pages that are listed. Or, if there's another word for what you're looking for, look up that word instead. You may find better results.