I just need some sort of programs that can download flv from website like youtube and other.
Video Download Helper is the best.
There is also youtube-dl. It's a command-line tool. The best feature of this tool is that it can accept a batch file as input. Besides this, it has many other features.
Be sure to install the latest stable version, not the one in the Software Center. Link: https://launchpad.net/ubuntu/+archive/primary/+files/youtube-dl_2011.08.04-1_all.deb
youtube-dl -ica http://www.youtube.com/watch?v=F1VezJENet8 -o "%(title)s.%(ext)s"