The Communist Manifesto isn't what I'm talking about. The CM is a worker pamphlet, not an explanation of Marxism. The Principles of Communism is a much better introductory work, and for Marx himself, Wage Labor and Capital as well as Value, Price and Profit are excellent texts describing Capitalism. I would also add Socialism: Utopian and Scientific for an introduction to Historical Materialism, and the failures of Utopian Socialists like the Owenites.
Lenin is absolutely worth reading, he was the leader of the first genuine Marxist state, and his contributions to Marxist theory are critical. Specifically, Imperialism, the Highest Stage of Capitalism furthers Marx's analysis into the modern era of Monopoly Capitalism, aka Imperialism, which Marx was only alive to see the very beginnings of before he passed away.
To be fair, most people on Lemmy.world can't either. The vast majority of people in the west have not read Marx, or if they have done so, they have only read the Communist Manifesto perhaps once. Communism is so thoroughly demonized in the Imperial Core that only a minor fraction have even read Marx, and only a fraction among them have read more than just the CM.