In order to this addon work, you need to enter your YouTube API KEY.
First, go to your c5's dashboard/system/ounziw_youtube_latest_video/settings
If you have your API KEY, enter it. If not, get your API KEY on google.com
After you enter your API KEY, go to the page and put a "Youtube Latest Video" block, you will find a prompt.
Enter your youtube's username. (In the above example, concrete5cms)
Optionally, you can set a default output data in the textarea. It will be outputted when it fails to pick up a youtube video. (ex. You don't upload any videos, or you entered a wrong username.) The data will be outputted without escaping.