This article doesn't indicate that he knows what tariff mechanistically does. Only that it will take inflict some amount of suffering on American citizens and possibly force manufacturing back into America.

He knows how they work: he threatens them and his supporters cheer, he implements them and people negotiate. There are other, some would say better, ways to get the same effects but tariffs are Trump's go to. In the metaphor "when you have a hammer everything is a nail" maybe Trump is the hammer and tariffs the nail?

I'd say tariffs are a hammer, every international issue looks like a nail and Trump is the simpleton that keeps swinging.