MMT is a description of how the currency system works in sovereign nation-states having a fiat currency and denominating all their debts in that currency. That’s a one-sentence definition requiring an essay to understand if you’re not an expert in macroeconomics and yet free from the BS orthodox economists teach; they are stuck pretending the Bretton Woods monetary system still prevails. Because of this error, traditional economics has no working model of inflation. What they claim drives inflation occasionally does but often does not. On again/off again isn’t how scientific explanations work.

But if you still want a Medium article on MMT, you’re in luck.
https://jameshollomon.medium.com/money-why-everything-msm-says-about-it-is-wrong-77df8a0df5e0

If you want a book, Prof. Stephanie Kelton’s new offering, The Deficit Myth, made the bestseller list.