Anyone may look along the shelves; only the librarian works the desk. There is no password: you choose who you are, and the database decides what that person may do.
1. Look along the shelves
Open Library, then Books: each book, how many copies are out, and with whom. Members shows who holds what, and Loans is the file, line by line. You need not sign in for any of it.
2. Sign in as the librarian
Press Sign in at the top of the menu and choose Princess Irulan, the librarian. The menu now shows the Desk.
3. Lend a book
Open Desk, then Lend a book. Type a book and a member, for example book BK000003 (Children of Dune) and member CU000092 (Paul Atreides), and press the round button. Lend the same book to the same member again: the database refuses, because Paul has it already.
4. Reverse a mistake
Say the book went to the wrong member. Open Reverse a mistake, type the same book and member and a reason, and press the button. Then open Loans: the loan and its reversal stand side by side, with your reason. Nothing was deleted.
5. Take a book back
Take a book back works the same way: Stilgar has BK000001 (Dune). Try taking back a book a member does not have, and read the refusal.
The demo starts fresh every night, so try anything you like.