"I read books."
Translation:Io leggo libri.
My boyfriend is italian and he says if you put leggo i libri...you are specifying the type of books vs just saying I read books. (Leggo libri) So you would most likely elaborate and say "I read the books by Shakespeare " vs "I read books" which is more general and without the word "the"
It is very complicated, unfortunately. See: https://forum.duolingo.com/comment/1012366/When-to-use-the-definite-article