To find your invoices, click on the user icon at the top-right hand corner of the page and select Billing from the drop-down menu.
Once on the billing page, on the left hand of the page is a Last 5 Invoices section. Click on the dropdown in the top-right corner and select View all Invoices to get a full list of previous invoices.
To download your invoices, look for the small printer icon when viewing an invoice. It can be found in the bottom-right corner.