How to download youtube videos onto my mac easily, and for free?

I play multiple instruments and i would like to make a cover video of me playing all of the instruments, in one video. I've seen a lot of other videos where its done,but i'm not sure how to do it in windows live movie maker or if it is even possible in windows live movie maker. I think it can be done but I just have no idea how. Please give specific instructions on how or a different program where i can do that.

I mean to Write on a CD OR DVD disc some Advise need.
Appreciating For Kind Answer,Thanks...

have loaded my videos on to my computer but when i load to dvd programme they are upside down

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I am making a couple copies of my DVDs to give to my friend as a grad present. I was wondering how to make the copies using a windows computer. I still want mine to work and have a copy if that makes a difference.