How do you download a You Tube video to a mac

Hi There is a software free on the net called YTD, which after some time they keep asking you to upgrade all you do is say no and continue using it free . all you do is open the software YTD start the YouTube video copy the URL starting from WWW. than click on download in no times you will have the video. May I suggest create a folder say on the desktop I called it Briefcase and in the software direct the downloads to that folder and that is all , good luck and enjoy it.