ISBN Agencies provide authors with an ISBN number.
The Bar Code is the graphic with vertical lines that is found usually on the back cover and encodes numerical information for scanning purposes.
QR Codes are those black and white pixelated squares that you sometimes see on posters, signs and other places. By scanning the code with an app on your mobile phone, it will take you to a particular website. They are considered outdated.
Tip #1: You need a Bar Code only if you plan to sell your book in bookstores.
Tip #2: Get your own free Price Specific Bar Code (different from the one provided by Create Space). Simply go to https://www.lightningsource.com/covergenerator.aspx and follow the steps. Note that each time you'll change the price of your book, you will also need to change the Price Specific Bar Code.