In most countries the publisher of a new book sends copies to the national library, and sometimes to other libraries too, so the country keeps a record of everything it publishes. When you publish yourself, you're the publisher, even if a store abroad prints the book on demand.
The studio reads the rules of the country you publish from, the one you chose on the ISBNs page: how many copies, where they go, by when, and anything the book must carry first, such as Spain's legal deposit number. The Uploads tab shows them beside your print formats, and once you mark one live in a store, it says by when the copies are due. When you've sent them, mark them sent there or in the launch checklist.
The rules come from each national library's own pages (or the law itself), checked on 1 November 2026; each card links to its source. They aren't legal advice. Where we haven't read a country's rules yet, the studio asks you to check with your national library rather than guess.
What you need: to choose where you publish from on the ISBNs page, and to mark each format live in the upload tracker when readers can buy it.