Content-related questions about individual lectures can be asked below the web player in the forum. The questions are forwarded to the respective lecturer and answered as soon as possible. You will find the answer directly in the forum.
To add a new comment click on the "+"-symbol on the right under the video player.
To view older comments you can click on "show all".
If you check the box under your comment you'll get a mail for each new comment on this lecture.
In case a mistake attracts your attention, there is a "report mistake" button below the lecture. To provide a better service it would be very helpful for us, if you report the issue.