This will open the Invoices tab automatically where you can see all of your invoices. Double-click or click View to open any of your invoices to see more details.
To download an invoice; select any individual invoice and click Download. You may also simply click Download from the table (#5 below) to download an invoice. (Right-click and "Open image in new tab" to enlarge)
Confirm where you would like to save your download on your computer and you are done!