Locate the bar code on the back of your book.
Check above the bar code. There will be a number directly above it, after the letters "ISBN." Some ISBN numbers will be 10 digits long, separated by hyphens. However, if the book was published in 2007 or after, the ISBN number will be 13 digits, separated by hyphens.
Type your ISBN number into a database online like Isbn-check.com. This website will tell you if the number is correct. If it is not, the database will come up with other ISBN numbers that are similar and may reflect the correct number.
Check on a website like Amazon.com by typing the ISBN number into the Search box. If it is the correct number and if Amazon carries it, the book will come up on the web site.