Start wherever the money side of the business is jamming.
Pre-accounting and e-invoicing are not one button but several steps that follow each other. The headings below are the order of those steps: receipt, invoice, account, payment, month-end figure.
All of it is part of one panel; smaller topics such as defining services and items sit inside the related page.
Where to start?
The headings are laid out to be read in order, not to count features. If you are coming from a paper book or a spreadsheet, the pre-accounting page at the top gives you a map of the whole panel. If your system is settled and your problem is one specific thing, go straight to that heading; every page makes sense on its own.
Everything starts with the receipt: the sale and the expense are recorded, the receipt turns into an e-Fatura, the amount posts to the account, and the payment is followed by due date. Unless the receipt is kept properly the rest of the figures do not come out right, so this is the first habit that has to settle in the panel.
As the number of customers grows, the real question becomes who owes what and when the money arrives. Briefly, which question sits where: what did I sell is the sales and expense receipt, did my invoice go out is the e-Fatura page, who owes me is the account page, was it collected is the payments page, did I make money is income and expense tracking.