Marking your invoices as being ready for invoicing is simple to do.
To tag timesheets for invoicing:
Click Invoicing, then select Tag timesheets for invoicing.
Select the Client and press the Tab key.
Click Tag.
To select the timesheet(s) to invoice, click Toggle on the selected timesheets.
Click Tag for invoicing.
At the top, click Invoicing, then click Generate Invoices.
Select the Immediate frequency and click Process only tagged timesheets.
Click Start.