How do i save youtube videos to my computer?

i have Download Helper, but i don't know how to use it. i want to make a video, on windows movie maker, using others from youtube. but every time i try to save videos using Download Helper, when i get on Windows and click add video, the one i saved before isn't there. so, how do i save youtube... show more i have Download Helper, but i don't know how to use it.
i want to make a video, on windows movie maker,
using others from youtube.
but every time i try to save videos using Download Helper, when i get on Windows and click add video, the one i saved before isn't there.

so, how do i save youtube videos to my computer?
thanks =)
11 answers 11