> doesn't touch on the actual conjugation (ie. how to turn "drink" into "didn't want to drink"), nor on plain form (everything is in polite form)

The conceit of the article is that it doesn’t teach any meanings, it just teaches “how to append a suffix to a stem”. If this much is obvious to you, that’s fine, the article isn’t useful to you. It was difficult for me to understand ichidan/godan.

The article does not attempt to explain how to pick the suffix or what those suffixes mean.