To access your invoices, log into your account on the website and select "My Orders" from the main menu. From there, it should list all previous orders associated to your email address.
Below is a screenshot for an example.
At this stage, scroll down to the order in question, click the "Download Invoice" button under the Order Details to show the downloadable PDF invoice(s) associated with that order. The downloading invoice(s) function is usually available a few days after the item has shipped. The button may not show immediately. Below is another screenshot for an example.
Please let us know if you have any questions moving forward!