Fonts and typography are fun. Material Design is a framework (developed by Google) that basically geeks out on how to assemble your typographical elements together into a design language. If you're into fonts and typography, it's fantastic. It provides a theming engine, reusable components, and can pull different user interfaces together under a common design paradigm. I'd highly recommend looking into Borries Schwesinger's book "The Form Book" if you're going to be working with Material UI or are otherwise new to component design.