Basing a cinematic universe off of eighty years of comic book history is no small feat, and when there is so much source material to read, newcomers may feel overwhelmed when trying to approach it after watching the films.
Comics and graphic novels have a habit of being difficult to get into anyway, with Marvel's numbering system in particular being notoriously confusing. The company only recently (properly) releasing collected additions of their older tales.
Due to the aforementioned eighty years of history, it would be extremely time-consuming to compile a complete reading order for the entire Marvel comic universe, but for the sake of everyone's sanity we have a few recommendations to start you off on your comic book/graphic novel adventures.
You'll probably recognise some of the titles as being the same (or very similar) to their MCU counterparts, but, like many adaptations, the originals have some pretty blatant differences. For example, while the MCU is, for the most part, a brilliant, more grounded representation of Marvel's characters and locations, the comics do not share the problem Disney does: owning the rights to all their characters.