You can download not only youtube videos but dailymotion, metacafe all other sites video too. Basically what it does is if any site's video is played there, Video DOWNLOAD HELPER automatically recognized the playing video and it gets activated.
When there is no video playing, the icon remains gray in color and stable. But when it will sense any video playing in the site, it will get colored as shown in the picture and animation of icon begins.
To download videos, click "Downward AERO" shape button right side of its icon, then you will see your videos in numerous quality (if available), then if you hover on one of that option, you will get a download button to click. After clicking that button, your download will begin.
