In order to create a new invoice you need to go to AccountingInvoicesAdd invoice. You can add items manually to the invoice by inserting new rows or by clicking on the Add outstanding time/costs and select from the dropdown:

Add from Timesheet – creates an invoice based on tracked time
 Add from Expenses – adds expenses to the invoice, but make sure they have the same currency as the invoices.
 Add from Projects – creates an invoice based on flat rate projects
 Add from Tasks – creates an invoice based on flat rate tasks

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