Before the first invoice
Open Accounting → Settings and fill your legal name, GSTIN, address and the invoice prefix. Upload your logo. These print on every invoice.
Add a customer
Customers → New: name, GSTIN (if registered), billing address and state. The state decides CGST+SGST or IGST by place of supply.
Add items
Items → New: name, HSN or SAC code, unit, price and the GST rate. Items are shared with Quotes, Inventory and Field Sales.
Make the invoice
Invoices → New: pick the customer, add items, check the tax lines, save. The number is assigned in sequence and never reused. Send it by mail or WhatsApp with a payment link, or download the PDF.
What happens in the books
The invoice posts to Books on save — sales, output tax and the receivable. A receipt against it posts the payment. Your CA sees a current ledger without anyone re-entering it.