mkv file extension

i’ve downloaded muse but when the file was on my computer i couldn’t watch it because it’s a mkv file. i tried to find some codec for it on the interet, but the things i found and tried didn’t work properly.
does anyone have a better idea?
cheers

mkv is a matroska file. you can find everything you need on this page
http://www.matroska.org/downloads/windows.html
(I personally like using media player classic.)