Stock moves from documents, not from typing a new figure over the old one — which is why a count that disagrees with the books is recorded as its own entry rather than overwriting anything.
Purchase → Purchase Orders → + New to place the order (Silver and above). When goods arrive, open the order and use Receive — it becomes an ordinary purchase bill carrying the order’s reference, so the stock and the supplier’s ledger only move once.
Sales → Sale Orders → + New (Silver and above) — for a promise you have made to a customer, as opposed to a Purchase Order, which is a promise a supplier has made to you. It needs a named customer, and delivering against it is an ordinary sale invoice carrying the order reference.
Books → Stock vouchers → Physical Stock lets you enter what you actually counted, item by item; the difference against what the system shows is recorded as an adjustment, with a reason. This is the correct way to fix a stock figure — never by editing an old bill to make the numbers match.
Books → Stock Analysis has views for everything in hand, what has not sold recently, what is at or below its reorder level, and what is expiring soon. The reorder screen (Books → Reorder Suggestion) goes further — it groups by supplier and works out roughly how much to order from your own sales pace.
Yes, on Silver and above — Purchase Bills → "Upload bill" reads a PDF or a photograph of a supplier’s invoice and maps each line to your item master for you to check before saving. It runs entirely on your computer, with no internet needed and nothing uploaded anywhere; you still press Save yourself, exactly as if you had typed it by hand.
Vouchers → Receipts / Payments / Contra covers most of it: money coming in, money going out, and transfers between your own cash and bank accounts. A Journal Voucher (for something like depreciation, on Silver and above) is for an accounting entry that is not a plain payment.
Press Alt + A in Aned Book and ask in your own words. It runs on your own computer with no internet and no account — these pages are that same help, published so it can be found before you install anything.