You need a barcode font, and then you type in the codes the same as you do letters
I don't have one where I am now (retired) but I used one at work to create labels for a barcode scanner
I don't remember the "exact" font name or vendor, but "code 3 of 9" sticks in my mind... use Google
Hi John - Many thanks for heads up on fonts. I've just downloaded a 'code 128' version of a barcode font as this is what my supplier's equipment uses/reads. I've sent them a test sheet to see how it goes. Fingers crossed!