ISBN Number and Bar Code
You will need an ISBN number and bar code if you plan to sell your books through a bookstore or Amazon.com, etc. EAN is another name for the ISBN bar code.
Bowker, is the US ISBN agency where you can obtain a ISBN number. Once you have the ISBN we can make you a bar code for free, to be placed on the back cover.
Why Do I Need An ISBN Number?
The ISBN number provides a standard way to identify your book, especially for bookstores and libraries. You will need an ISBN number and bar code if you want to sell your book in any kind of bookstore, either bricks and mortar or on the internet.
The ISBN number ties into a catalog of all (registered) books in print. This catalog lists the publisher, access and purchasing information, and descriptive data about each book.
As a grammatical comment, "ISBN number" is redundant; "ISBN" means "International Standard Book Number", so "ISBN number" is "International Standard Book Number number". But it's common to say number anyway.
For more information on ISBN's and how they work please visit https://www.myidentifiers.com