Well, one theory is that Trump wants individual companies to come to him and beg for exemptions to the tariffs. This would consolidate his power: Nobody would dare to do anything that would oppose him, for fear of having their "tariff exemption" revoked.
Another theory is that Trump has some complicated plan to reduce the US's debt; again, it involves using tariffs as a "stick" to push our allies into doing what we want. Summarized here:
Trump take bribes with companies and countries for exemptions to tariffs. Trump informs insiders of upcoming market manipulations so they can exploit the falls and rises. Inflation rises in the us as companies have fewer competitors and another justification for price increases. Income inequality increases just like the last guy that said lets make america great again.