IonandHomer

Plato's Ion

First, the lead character, named Ion, is said to be a prize-winning member of a long line of and guild of rhapsodes, bards who sing the Homeric poems.

We don't know if such a person named Ion really existed, because we only find him in this one work, but there were contests and prizes for such things.

Overall, philosophically, this is one of Plato's several way to take on the strong Greek belief that Iliad and Odyssey were not just a part of the education of a Greek (man), but a chief part, and indeed that they were a source of wisdom and knowledge to Greeks.

Plato indicates elsewhere that he does not think they deserve that place in Greek education: he even bans them from his republic.

530c: the rhapsodes as a group, and Homer, are built up as cultural touchstones of great importance.

Iliad and Odyssey are quoted by a wide enough variety of movers and shakers in Greek culture that this is clearly seen to be true outside the dialogue.

531b: if different songs differ about some matter, who should decide between them, the singers or the experts on that matter?

This is Plato setting up the idea of specific knowledge-based expertise: a challenge to the idea of song-based broad cultural expertise, somewhat parallel to the idea that the Bible is the only book you really need.
It's not that Homer can instruct us in divination or ship-building, but rather that knowing Homer serves as a sort of touchstone, a cultural indicator of being educated, and weaves together all manner of things such as divination, ship-building, and many other things, in a way that is important and relevant.

531 mathematicians, rhetoricians, nutritionists and doctors: they know better than Homer-bards about mathematics, rhetoric, and nutrition.

Note that these sorts of specific niche experts are arguably not there in an 'oral' culture

THIS IS PART OF A SHIFT OF PARADIGM from an oral/song culture to a culture based on writing, prose, and specialist expertise: it takes a long time to make that shift, and, for some good reasons, it never really fully occurs (witness various ways that the 'experts' fall short, and how song/literature is still an important way for humans to process the world).
533c: Ion agrees with Socrates, but then asks, reasonably, how it is that he himself, Ion, is so good at Homer, but not at the other poets: how does he 'come alive' and win important prizes if not via his skill, expertise, and knowledge of what Homer writes about?
533d: Socrates replies that it's divine inspiration, like a magnet: it starts with Homer himself, and passes its force thru all the subsequent singers. It's divine, not something a human can understand or explain.

Elsewhere, in Gorgias, Socrates suggests to Gorgias that there is no expertise of public speaking or persuasion: it's a knack, not something teachable, not something knowledge-based.

535c: a last tidbit that is relevant to our class: the Homeric songs were emotional and alive to their audiences.

The chief point of reading this dialogue is to access some widely held ideas about Homer: Plato would never have written about this if it had not concerned him, and it would not have concerned him if he was writing about a one-off peculiar quack. He was taking on a large part of Greek culture, namely Homer.