How the application works, screen by screen — and four worked setups you can copy. Everything here describes what is in the product today.
If you are starting from nothing, read the quickstart, then core concepts. Between them they cover the whole loop: upload documents, write a question per column, run the table, check an answer against the page it came from.
If you are evaluating rather than using, how credits work and tiers and limits are the two pages that answer what it costs and what it will not let you do.