If you want the basics of modern literary theories, you will need to know two movements. The first is modernism, and the second is postmodernism.
Even though modernism is difficult to define, we can make a few generalizations.
Modernism rejects the past. More specifically, it rejects the 19th century – the Victorian era. Second, Modernists reject an epistemology of any absolutes. Third, modernism is influenced by Freud’s psychoanalytic theories. In a nutshell, Ezra Pound's famous statement "Make it new" encapsulates much of the modernist movement.
Postmodernism takes things one step further. Postmodern literary theory rejects any sort of meta-narrative, which includes traditional ways of thinking and any single way of viewing reality. Even modernism is too structured. Instead, reality, according to postmodernism, is malleable and flexible.
Post-modernism also emphasizes ideas of deconstruction, disintegration, and multiculturalism. This makes sense, because all of this goes against the idea of a grand narrative. To use Foucault's languages, there are archaeologies of knowledge.
All of this is just a basic sketch. Any movement is hard to define and there will always be fuzzy borders.