I had trouble with this. The editing pane was on the bottom, not the left, and problems would expect an answer that would have required me to be psychic to answer. E.g. I was supposed to type in foo but foo wasn't mentioned in the problem.
I also found some of the questions required thinking a lot harder than what was strictly required for teaching a concept.
But after a couple of questions I really got into it. Compared with the section in the Nix manual, I found it much easier to pick up the language.
The issue with the editing pane might be related to the size of the browser window. It splits horizontally at lower window widths, just like tour.golang.org for example. But unlike the Go tour, it splits at a much higher window width than strictly necessary.