There are several plug-in that generate different kinds of barcodes, google filemaker barcode plug-ins.
Here is a link to create Code 39 Barcodes without a plug-in http://www.excelisys.com/blog/2013/11/20/filemaker-pro-code-39-barcode-generator-without-fonts-plug-ins/
Barcodes are just ID codes formatted with a special font so you really don't need a plug in if you are able to install the right fount and calculate the needed "check digit" to append to your ID code for the type of bar code that you choose to use.
What you do next depends on your hardware. You can scan bar codes with a BarCode scanner that functions in Keyboard Emulation mode that connects via USB to your computer. You can scan bar codes (This is slow) with the camera of an iOS device using FileMaker Go or you can attach a blue tooth scanner to your iOS device.
How you set up your scripts to process scanned bar codes will depend on the hardware you use for scanning.
Here's a link on bar code scanning with a scanner connected to your computer via the USB interface: Need help writing script to integrate barcode scanning
Thank you Chamblee. I did Google the issue. I just wanted to see if anyone in the forum had any personal experience and recommendation before I spend on a plugin. Unfortunately we are stuck with code 128 since it is our customer requirement.
PhilMod, I don't need to scan. Just convert two fields from my purchase orders into barcodes to print on a label. Thanks.