printing labels

Does anyone know how to print labels with a barcode to put on our books?

Depends on what you want. I once wrote a small script to generate pdf-files with 24 (I think) barcodes on each page for out local library. It was designed to fit on a label sheet. You need to consider how permanent you want the solution to be. (i.e. a laserprinted handmade label will probably fade away in a few years and placed on the outside of a book it could fade in a few months). The barcodes can be encoded in one of several systems so you also need to decide which one you want and if you want some text on the label too. With a bit of luck someone will have something usable in say Excel, so you can roll your own barcodes without really knowing what is going on :-) Google for "How to generate barcodes in Excel?"

I'm not sure what became of my script, since I haven't used it for more than 10 years.

Another option might be the printed bar code labels sold by LT: https://www.librarything.com/more/store/barcodes