If you close that window using the "x" in the upper right hand corner I think you can go into purchases, like Diamond Girl suggested. Then click on the item and the option should be there to leave a review. One caveat though: on my etsy store the option to leave a review doesn't pop up until the expected delivery date has arrived/passed, so it the shipment arrived "early" it just might not be up yet. There is a way to go in and do it manually, but if you can't get there don't worry because the system should start popping up reminders to leave a review in a day or two.
ETA: Thank you for doing this BTW -- we really appreciate reviews!
If you do what @Dee*Jay suggests, and click on purchases, the option for leaving a review is there. I actually get pop-up reminders that appear at the top of the page. It shows a pic of the item I ordered and empty stars. You click on the amount of stars you want to give, and you just follow the prompts for rest. Just as Dee*Jay said, sometimes you have to wait before giving a review, but I think it's thoughtful to do so.