so much interface fail
But I'm not easily deterred so I did manage create an account and to upload the image, finally, but then when I wanted to do the simplest product design, i.e. pick a card, put the image on the card sized so that it fits, without even any text or borders or stuff, it constantly did weird things. Like I wrangled it right, and clicked the save, but then back in the overview it had saved empty. And then when I finally managed to put an image onto a card, and made it public (or so I thought), it didn't show on the shop page, which I thought was because I got a page error in the middle and had to reload. However, it seems that was just a time delay, but they could have said that it takes time to show up.
Also, whenever I clicked the help popup to explain something I only got the general main help page. Like there would be a link "what is such-and-such" to explain a function and then I didn't get somewhere that even had the term on the page.
However, I did manage to create a Santa!Cthulhu card, and I think one can replace the country code in the zazzle URL with the one most convenient, like pick the .com ending for the US store.