If you didnt know that, I would HIGHLY suggest reading
THIS DOCUMENT, outside of some the advice, everything I wrote came from there.
It also gives you all the criteria that they are going to judge you against, so if any of those criteria are missing from your essay you can use your presentation to cover that.
Also note that they may never see your video, so DON'T rely on it telling more of your story. They may only use it to display if you win.
Good luck!