Friedrich Engels - Principles of Communism - Accessible FAQ-style introduction to capitalism, communism and other key Marxist concepts. If you're completely new to Marxism, this is the best one to read first.
Joseph Stalin - Dialectical and historical materialism - A very succinct introduction to the Marxist method of investigation. This text has a few problems with economism viewing production as being a hard determinate of social development, but is still worth reading to understand Marxist materialism.
History is Marching, a 2-hour documentary outlining our contemporary material conditions at the international level, and the threats we face such as great power competition and climate extinction. It is available in chapter-sized chunks on the Prolekult channel.