Type an ISBN-13 and download its barcode: the EAN-13 bars at the standard size, the digits below and the ISBN above, as a vector PDF or SVG for your cover, or a high-resolution PNG.
KDP prints a barcode for you in the box on the back cover if you leave it blank, so you only need your own for other printers, or to place it yourself.
What you need: an ISBN-13 from your national agency.