If you are planning on distributing your paperback or hardback outside of Amazon (for example, in brick and mortar stores), you will need to provide a barcode on your book cover. Formatting requirements can be found here: https://kdp.amazon.com/en_US/help/topic/G5HDYGP4BXLX4RUW#formatting
Barcodes are not required for e-books.
Amazon can create barcodes for you as part of the upload process, even if you bring your own ISBNs. Alternatively, barcodes can be created by putting your ISBN into a barcode generator, which can be found by Googling ‘free barcode generator’.