How do I generate a list of one-time passwords?

a very novice programmer here. I am currently working on a website in which I would need to create a password-protected section. The passwords should be single-use only, turning unusable after entering succesfully. OTP seems to be the way to go, but I cant find guides on generating lists of passwords for the OTP, just ones that teach how to send SMS or use a separate software. The security of the website doesnt have to be hacker-proof, just secure enough that the average joe doesnt know how to abuse it.

Probably im missing something obvious here, but help would be appreciated.