Plato deals with the question of the relationship of poetry to reality in two major dialogues, Ion and Republic.
In Ion, the Socratic character criticizes the rhapsode Ion for claiming to know about things like generalship from reading Homer. Since Homer is using words to discuss generalship, and Ion using more words to comment on Homer, Ion is remover from the reality of war by two levels of reality, and therefore should not claim the ability to advice the Athenians on war (or any other topic).
In Republic, the Platonic Socrates critcizes both painting and poetry as mimetic arts. In painting a bed, for example, the painter imitates by means of paint a bed made by a craftsman. The craftsman's bed, though, itself, is merely an imitation in wood of an ideal bed in the craftsman's mind. The poet imitates by words as the painter by paint. What the poet imitates are the phenomena of experience, which themselves are merely imitations of the ultimate divine forms.
When studying this, pay particular attention to Books II and IX of the Repuiblic and the allegory of the cave.