Click on "Window" -> "Billing" to open you invoice manager. The invoice manager includes your quotes, your invoices and your invoice reminders.
Here you find an overview of all created invoices. There's multiple filter and grouping options you can use to print the report you need. Mark your invoices as paid, as soon as you receive the money, then you'll have a good overview of all your invoices.
To mark an invoice as "Paid", right click on the invoice. Hide and show columns by right clicking on the column header.