I’d recommend Principles of Communism (specifically question 17, though the whole pamphlet is tremendously useful) as well as Socialism: Utopian and Scientific from Engels if you haven’t engaged with Marxist theory before. S:UaS does a great job of elaborating on Historical and Dialectical Materialism in a short form-factor, elaborating on the why of Communism to begin with, essentially working with analysis of present systems and predicting forwards, as opposed to coming up with a “utopia” and working backwards.

If you want a Marxist analysis of Capitalism and why it will prepare the foundations for Communism, I recommend Wage Labor and Capital as well as Wages, Price, and Profit if you want the short version and don’t want to read Capital.

I also have a beginner Marxist-Leninist reading list I curated for easy sharing.