Honestly, I’d start with Blackshirts and Reds, it’s a history book that analyzes AES states critically and debunks modern anticommunism and anti-Marxism. Michael Parenti uses modern, non-Marxist language to appeal to liberals and leftists sympathetic to Marxism but unsure about it and AES. An alternative, or supplementary source, is the famous “Yellow Parenti” speech and/or Albert Einstein’s Why Socialism?

The absolute best primer is Engels’ The Principles of Communism, which I would follow with Politzer’s Elementary Principles of Philosophy, and swing back to Engels for Socialism: Utopian and Scientific. From there, you should understand what Communism is, how Marxism diverges from older Socialism, and Dialectical and Historical Materialism, the philosophical foundation of Marxism.

Now, you can read Wage Labor and Capital as well as Value, Price and Profit back to back for Marx to explain the Law of Value, and prep you for Lenin’s works Imperialism, the Highest Stage of Capitalism and The State and Revolution, to bring you to the modern era of Imperialist Capitalism and explain the Marxist theory of the State.

If you read all of those works, you will be more well-read than the vast majority of Leftists. There are numerous other fantastic Marxist works, but this will get you by far the most bang for your buck.