Fantastic that you have uploaded your first assignment! It does not appear to be working correctly though, so lets see if we can sort that for you. The best way to upload your video is to youtube, then copy the link and past into the forum. I find it easiest to upload straight from my phone to youtube, with an "unlisted" setting on youtube, which only allows those you have shared the link with to view it. YouTube converts it to the correct format that allows your coach to do you voice over feedback for you.
See how you go, and if you need more help with it, please don't hesitate to ask.