What does this actually explain that the spec does not?
An OpenAPI document is written for machines, and reading one to work out whether an API does what you need is slow. This explains the document instead: what the API is for, how it authenticates, what the error model looks like, and where the surprises are. You choose the angle — a short overview, a technical integration brief, a resource-by-resource walkthrough — and can keep asking follow-up questions about the same document.
Which specification versions can it read?
Swagger 2.0 and OpenAPI 3.x, in either YAML or JSON
Can I ask follow-up questions?
Yes — the specification stays in context, so you can keep asking about the same document
Does it need a complete specification?
No. A partial or sparse document still gets an explanation, including what is missing from it