Head over to the invoicing tab, under invoices, click on "New Invoice" on the right of the screen.
A popup window will open for you to select the desired project and commitment:
The invoice details page will now open populated with all the line items from the SOV. You'll have to enter the period quantity for the invoice by scrolling to the right. You can chose to enter either the period quantity, or the period amount, or the percent to date. The two other fields will automatically calculate.
When you are ready, click on "Start approval process", this will start the workflow for invoice approval. Click here to see how to set up workflow rules.
You will then be asked to confirm the billing period:
Click "Confirm and send". The invoice will now appear in pending approval status!