The article describes how CRT is a means of understanding how racism still shapes all our institutions (especially legal ones) and benefits white people. Europeans, settling in colonies around the world, violently appropriated land in places where they did not come from, committing genocide against the people who lived there - which still shapes the lives of the people who survived that genocide. It also made those people into a single race that were regrettably wiped off the face of the earth (despite having a diversity of culture and still existing).
They also stole other people from their homes and pushed them into brutal version of slavery that made the enslaved into a racial caste to better control them (Black people, rather than the diversity of different people and cultures that existed back home). They then wrote laws to ensure that those people would be oppressed even after slavery.
All that shapes our legal institutions to today.
They also rewrote history to leave out all the brutality committed against people who they said were less “evolved” than them and were of a “different race.” That historical narrative says that what happened was for the best, despite the millions of human beings who suffered and continue to suffer, and that the actions of people who came to call themselves “white” were entirely justified, as they were more civilized than the people who they brutalized. The people brutalized are expected to be grateful for being given the “gift” of western civilization because they were “people without history” - another lie as the people who were victims of European colonization had their own histories and civilizations.
CRT calls all that what it is - racist bullshit and seeks to correct the historical record and to show that these attitudes STILL pervade all our institutions and will continue to do so, as long as white people continue to believe them and to hold most of the power in our societies. It’s not calling white people evil, it’s saying that people who embrace that narrative are believing in a lie.
TLDR - racism is a historical construct that works through political, legal, and social institutions primarily for the benefit of people deemed to be “white.”
OR… go RTFA. It’s a pretty straight forward explanation of what the theory is and how it explains the racism of our modern system.