Illiteracy is the inability to read. You can help someone overcome illiteracy by reading together, or even by sharing your knowledge of vocabulary.
The word literacy means “the ability to read.” By adding the prefix il-, you change the meaning of the word to its opposite. Illiteracy can refer not only to the inability to read but also to a lack of knowledge in other subject areas. If you’ve never heard of Shakespeare, some people might consider you culturally illiterate.