I don't know your industry is but "barcodes" is a pretty big topic by itself in that there are many fields you can encode into the bar code. For a 2D barcode, you typically have a prefix which indicates what info will be following it eg/date code) or vendor part number.
If you are going to be supplying direct to a business, then they typically tell you what information they want encoded and how big it needs to be. An outer shipping box will have 1 level of data, an inner shipping box will have individual lot level information. They tend to have general specifications which say what they want on it. In my company we have two bar codes - 1 for our usage and optional 2nd which is then customer specific.
Much of our barcodes are now 3D as you can get more info on them.
All my experience is business to business and we don't put anything on packages for retailers.