Per active user per month, in US dollars, at one rate worldwide. Every package keeps the full double-entry ledger, banking, selling and all 29 reports — what changes is how much of the supply chain you run.
If you sell services and never carry inventory, Books covers you.
If you buy goods, receive them and pay supplier bills, you need Business.
If you cost work job by job and invoice from the project — or you want to collect ratings, testimonials and documents from your customers through secure links — choose Advanced.
The full commercial terms — how users are counted, billing periods, package changes, renewal and cancellation — are in the offer details. More answers in the FAQ.