How can I print a free online barcode generator onto my products by using barcode generators?

I’ve know about the barcode generator for a long timeand even have managed to generate different types of barcodes and even managedto generated several barcode by myself. I also searched some free onlinebarcode generators ,  such ashttp://www.keepautomation.com/ and it is very useful. But , how can I  print a free online barcode generator onto my products by using these barcodegenerators?