That’s a good question. There is one simple way…

Step 1. Go to http://en.getvideo.org/
Insert your Video URL in the special field and press “Download video”.

Step 2. Select the format (mp4, webm, audio, 3gpp, x-flv) and quality (480p, HD, FullHD, UltraHD).

Step 3. Start download video from YouTube.

GetVideo.org is a free online application that allows to download videos from YouTube and Vimeo for free and fast. It is a simple web service to download your favorite video in different formats (mp4, webm, audio, 3gpp, x-flv) and quality (480p, HD, FullHD, UltraHD).

Look some videos about downloading from YouTube: