Which barcodes it reads
EAN-13 and UPC-A are on almost every product in shops, and EAN-8 and UPC-E are their short forms for small packs. Books carry an EAN-13 that starts with 978 or 979, which is the ISBN. Code 128 and Code 39 hold letters and numbers on shipping labels, asset tags and badges, and ITF-14 marks outer cartons. QR codes are read too, with the same link checks as the QR scanner.
What the check digit tells you
The last digit of an EAN, UPC or ITF-14 number is worked out from the others, so a single wrong digit or two swapped neighbours shows up straight away. A verified check digit means the number was read or typed correctly. It does not prove the product is registered, and the GS1 prefix shows only which country's GS1 office issued the number, not where the product was made.
Getting a clean read
Hold the barcode level and close enough that it fills most of the frame, in even light without glare. Curved bottles read best when the bars run up and down the curve. If the camera struggles, take a sharp photo and choose it instead, or type the digits into Check a number.