I guess what is considered easy is very subjective. I seriously think Marx' Manifesto of the Communist Party is not a bad place to start. It's everything Capital is not: short, easy to read, somewhat superficial.

I'd say the historical analysis is at the core of marxism as much as the economic one, and it's summarized perfectly right from the start:

The history of all hitherto existing society is the history of class struggles.

Freeman and slave, patrician and plebeian, lord and serf, guild-master and journeyman, in a word, oppressor and oppressed, stood in constant opposition to one another, carried on an uninterrupted, now hidden, now open fight, a fight that each time ended, either in a revolutionary reconstitution of society at large, or in the common ruin of the contending classes.

Make sure to take a second to reflect on this and the Soviet Union and the failure of Marxist-Leninism. It was not the end of history, but another common ruin. Which brings me to the biggest problem of studying socialist theory: The line between theory and propaganda is often blurred. The Manifesto of the Communist Party itself, thought-provoking as it is, is a pamphlet made for wide circulation, and more propaganda than academic work. Marx' understanding of history revolves around how proletarian revolts such as the Soviet Union go wrong and end up reproducing existing power structures. Yet many of today's self-proclaimed Marxists are somehow blind to this and end up tricking themselves with all sorts of mind games.

That's why I think it's important to start with Marx himself. Understand his view of history and his criticism of the economy, and reflect on what it means for what you see in history since it was written. It still holds, though the theory itself has become weaponized in the very historical and economical dynamics he is describing. If you understand this independently you're less likely to become a sucker who falls for propaganda.

And of course, Marx wasn't a god, and he didn't get it all right. I personally think the main problem is his understanding of history as having an "end" (a teleological account) - Marx believed every class revolt would lead us slightly closer to a classless society, and that eventually we would get there. This builds on Hegel, who had a similar understanding of history rooted in religion rather than communism. I think this is plain wrong - things very well might just get worse, and there is no end of history. But that's me.

Of course one shouldn't focus only on Marx, but I feel like he's important enough that it's worth taking him seriously. And with all the stupid takes people have on his work, I think it's a good idea to go straight to the source.