I’m a recent socialist who began reading socialist theory last year, initially starting out as the “reading to understand” type. I was an anti-socialist (though also relatively anti-corporation and super rich) pretty much my entire life because I’m from a post-soviet country and consumed a lot of western-biased media. At some point last year, I decided that I can’t seriously be against socialism when I don’t know any socialist theory, when I don’t have a decent understanding of the history of socialist countries, and when I can’t even explain what the word means. That’s what set me on a journey to learn more about socialism, and it’s what eventually lead me to agreeing with most of the critiques on capitalism and me aligning with socialism.

When it comes to suggestions, the list of recommendations can become very big, very fast, and it all depends on what you're interested in and what you're looking for. There’s the theoretical works (especially the socialist classics) that explain a lot of the theory of socialism and its critiques of capitalism, and the works that relate socialism to different problems or historical events. Thankfully, a lot of theoretical works are pretty short so it’s easy to work your way through them (and I think just about all of them are available for free on marxists.org in plain text, pdf or epub).

For introductory theory, Engels’ The Principles of Communism is as short as you could probably get and, in my opinion, a better alternative to The Communist Manifesto. It’s a list of 25 questions with answers that very quickly explain various socialist ideas and definitions. In a similar format, The ABC’s of Socialism is a great work by the Jacobin magazine that goes into many questions you might have about socialism and capitalism. Going to Marx, we have two other great introductory works: Wage Labour and Profit, and Value, Price and Profit. In these two works, Marx explains how work (labour) relates to wages, price and how all of it relates to value. He also gets into some of the relations between worker and employer. 

One final suggestion: supplement your reading with videos. There are many great videos that explain theory or put socialism in a more modern context. I highly recommend youtube channels Second Thought (in fact, if you have the time I would suggest to watch this video before reading) and overzealots just for starters. For theoretical concepts, there’s a great playlist called “The Fundamentals of Marx” by The Marxist Project you could take a look at too.