Using this webapp is super simple: just type the name of the video or song in the search bar and click accept. Then you can choose the song or video you want from a long list, and set the desired quality of the output. You'll normally get different quality options adapted to the different devices compatible with the webapp. How long the video or song takes to download depends on the format you choose.
AvpTube is a downloading tool that's really easy to use and fetches your download of any song or video in a matter of seconds.