I clicked "just code" on the landing page and it took me to a page where the left pane showed an empty (black) terminal and the right one a python shell. Looking at the developer tools I saw a message in reponse to my hello world input saying that I should type 1+2. But it was never displayed.

Then based on this hint, clicking around I managed to reveal the tutorial (showing up on the right). So it seems that there is a bug in the navigation or maybe the "just code" link on the landing points to the wrong place.