The way FVD - Free Video Downloader works is very simple: it comes with an integrated web browser from which you can access any webpage to download videos. Once on the site, just select the video you want, give it a name, and save it to your phone's memory.
It's important to keep in mind that you can download tons of videos from tons of different portals, except YouTube.
FVD - Free Video Downloader is an interesting app for downloading videos. Its only major drawback, however, as mentioned, is that it doesn't work with YouTube. Luckily, there are many other apps (like TubeMate or YT3) for that.