Well, you have seen some videos from youtube in youtube.com or attached in blogs or other sites. But you didn't know how to download them, like this one that we can watch in this post. If you use firefox browser you can download an add-on: DownloadHelper. If you don't have firefox browser, you can download it here.
If you want to download directly from youtube.com, you should use this software: YouTube Downloader Version 2.1.6. Let's have some fun Guys!