The Legend of Zelda Collector's Edition

I assume your talking about Majora's Mask. If not, any masks in OoT are found as a child in Castle Town in the Happy Mask Shop. You'd trade them between people to get more masks. A total of eight in all.

As for Majoras Mask. Well...

www.gamefaqs.com/console/gamecube/file/919239/9396

that tells you where they are and how to get them.

There is the Deku mask. (It alaows you to be a deku scrub)
There is the Goron mask where you find at goron valley or somthin.
And there is the zora mask where you find it a zoras domain.

Those are the 3 masks i would define as magical, the others don't do anything. (at least i think so!)

If your talking about Majora, you're not asking much are you? My goodness! There are 20 masks scattered all
over the game, some requiring lengthy explanations on how to obtain them. I really think that is far too much
for anyone to answer here. I don't usually condone telling people to look elsewhere, but honestly!
Here's my recommendation. Go through the game and find as many as you can on your own. If you get stuck,
ask about specific ones you're having trouble with. More than likely, also, a walkthrough or FAQ somewhere
should have a comprehensive list. Also, I can't say this enough, when you play a game, write down everything.
That way, the next time, you won't have to guess. Then store your notes in a separate folder for each game or
put them in your computer. (It's what I do.)