Introduction to Marxism (Short Reading)
Marxism is a vast corpus, covering philosophy, economics, politics, sociology, history and even at times biology and physics. It is often hard to know where to start if you want to learn more. Even more complicating, because there is so much popular 'discourse' about Marxism, it is difficult to approach without being loaded with preconceptions - many of which are outright wrong.
When approaching such an expansive work, I think for my own benefit it can be useful to think about how one would go about teaching such a thing in a structured way. The following is a reading list I think would be very suitable for undergraduates without prior knowledge to complete over the course of a fortnight.
Wage Labour and Capital by Karl Marx
This is basically Capital 0.1. Simpler, far, far quicker to read (can do in a single sitting) but gets across the basic fundamentals of Marxist economics. I reckon online discourse about Marxism would be doubled in quality if everyone read at least this chapter.
Socialism: Utopian and Scientific by Friedrich Engels
This is basically Engels summarization of Marx's ideas and how it is "scientific" and materialistic compared to the other idealist and "utopian" socialist ideas of the day. At the very least I would recommend Chapter 3 which explains historical materialism. Again, a quick read you can do in an evening.
Marx only mentions the Dictatorship of the Proletariat around a dozen times in his entire corpus. In this pamphlet, Lenin explains socialism in practice and transition (again, easy to do in a sitting). It is perhaps this work more than any other that set the stage for Marxist-Leninist dictatorships that plagued the 20th century. If you are pressed I would recommend Chapter 5.
Those three are a bare minimum I would recommend for understanding the basics of Marxism. You can probably knock all three out in a day, and they are free online. If you haven't read these I would recommend not having super strong opinions about Marxist theory or getting into online slapfights about it.
If you are willing to spend a bit of money (or go to a library!) and spend a bit more time reading, I would also recommend:
Marx and Marxism by Gregory Claeys
More a history than theoretical work, Claeys traces the evolution of Marx's thought through time, providing invaluable contextualisation to Marx's work. You can get the 101 of Hegel and Feuerbach and other key influences without needing to read them, and cut through some of the more difficult jargon. If pressed for time, you can focus on Part 1 as Part 2 tackles post-Marx Marxism throughout the world.
Revolutionary Russia by Orlando Figes
No discussion of Marxism is complete without looking at the U.S.S.R, the first and foremost of the Marxist inspired states. This is another very, very easy read (another Penguin Introduction like Marx and Marxism) which traces the Soviet Union decade by decade from its revolutionary precedents through to collapse. I devoured this in an evening. It is just a good simple standard history. Again, if pressed for time, you can focus Chapters 5-8, which cover the core revolutionary period of 1917 and the Civil War.