You can find out invoices for your clients under 'Billing' view.
Invoices for the current month can be found under 'Draft' status.
To create invoices that are in Draft or waiting for an approval, you have 2 options:
1. Open the invoice, do the changes and create the invoice
2. Select the client in the invoice list and select from the header 'Create invoices'
Invoices from the previous period can be found under 'Approval'
When period has finished and some work has been done to the customer after that, select the client and click 'Recalculate'.
Send out created invoices
To send out invoices, select them and send out to your clients. If you want to send out the invoices from your email, then set it up under Billing app in the AppStore.