I just started and I think the site navigation could be improved. Please put numbers on the lessons. After each lesson, there should be a link to "next lesson". I see lesson titles on the right, but it isn't clear which one should be next. If they had numbers, it would be a lot more straightforward.

(Yes, I'm sure after a few more lessons while this will all become clear, but why not make it easy from the start ?)

Thanks.