Buy a barcode sticker printer, and normally it will come with some software to generate barcodes.

There are free programs to generate barcodes as well like zbar.

If you don't have a barcode sticker printer, you will need to printer the stickers on inkjet or laser printers, on precut A4 sized labels.

The barcode sticker label printers are very fast and easy to use. Usually, thermal printing with the ink coming from a ribbon. Looks very nice initially, but can smudged if you deliberate try to do so with your fingers, plus after about 4 to 6 months, some labels start to look "not so nice". Laser printed ones lasts longer.

As a retailer, I would use the barcode sticker printer. As a manufacturer, I would laser print. Perhaps there are larger sticker printers that use a laser print engine instead of a thermal print head.

You can just make up the numbers. If you want standardized numbers like UPC, there are organizations to register with to get your assigned block of numbers. The first few digits identifies the manufacturer, the final few digits identifies the actual product. Not sure who the organization is in Malaysa. You can use google. I suspect there might be a fee.

If you do create your own code, make sure it does not look like those standardized ones. This way, people know you made up those codes. The simplest way is to use a different number of digits. Other "make up your own codes" small manufacturers might accidentally use the same codes.

If a clash like this happens, and your customer is a small scale retailer, then no biggie. They call you to complain, you appologize, and print a bunch of new codes on stickers, and give it to them to stick over the products. After that , don't use the clashed numbers anymore.

If your customers are large supermarkets and hypermarkets, it'll be a disaster. They might stop ordering from you. Come to think of it, some large retailers wouldn't accept any product that don't have those standardized barcodes. If you just fake it and one day coke come out with a new bottle and new barcode, and happen to use your code, and they're selling for RM2 while your product is supposed to sell at RM8, the retailers might come to you and ask you to reimburse them for loses for selling those things at the wrong price.