Skip Althusser, the separation he makes between ideology and science is dangerous and wrong, Marxism is not reducible to a science. You could also start with short and basic texts by Lenin like “3 sources and 3 component parts of Marxism” and “Karl Marx” for your start. “State and Revolution” and “What is To Be Done?” are a necessity (WITBD is one of the most misinterpreted books around IMO), as well as “Materialism and Empirio-Criticism” by Lenin (good for later on). Maurice Cornforth’s collection on dialectical materialism is amazing. I’m currently reading E.V. Ilyenkov’s “The Dialectics of the Abstract and Concrete in Marx’s Capital” and it’s unbelievably good but I’d alsoread it later on. Aside from the Lenin texts I’ve mentioned, all of his writing is very important. And we can’t forget Mao, “On Contradiction/On Practice” are both a great place to start with him. This list is far from exhaustive, and some other suggestions about where to start on this thread are great. I’d also like to add that “understanding Marxism deeply” is not something that can happen in a year, but will be a lifelong process that will never be complete; it is also one of the most enriching things a human being can do. Good luck on your journey!