A barcode, simply put, is visual storage of data. Some form of identification is given to a product, such as a book, an item of food or furniture, and the bar code is created to show that data. Certain machines, such as scanners, can read the information and associate it with the product, simplifying purchases. Depending on the type of bar code, if you have a barcode number (which can be obtained when you create a product, such as a self-published book, for example), you can create the appropriate barcode almost instantly.
Obtain your barcode number. This can be done by registering your business for a unique range of numbers. For U.S. codes, apply to the Uniform Code Council in Dayton, Ohio. If you plan to do business outside the U.S., contact the EAN authority in the other countries where you'd like to do operate (see Reference 1 below).
Save your barcode number exactly as it appears. Depending on the type, it will have a set amount of characters, separated by hyphens. It is best to keep the exact formatting of your barcode number.
Visit a barcode generating website. A simple web search will bring up many results. For many of these websites, you only need to have your barcode number to complete the process, though for others you will need to select the symbology so it can create an image in the right format.
Input your number and select the appropriate barcode symbology. Generate the barcode, and you will be given an image you can save. This image can be printed or used however you like. However, if you edit the image too much, such as modifying the size of the barcode, it may not work correctly.