I got a new codec so I could play .mkv files, but.. I dont know where I need to extract it to (it's in a zip file right now). I tried reading the guide to codecs, but I dont think it has any answers for me..

I've never done this so.. yeah please, help?

Have you tried reading the guide on this site:
http://www.free-codecs.com/guides/How_to_i...nd_AX_files.htm

I installed it as they said to, didnt work though.

Did you download Matroska codec from official site? http://packs.matroska.org

Once you register/install the codecs, all you need is a directshow player like MPC, Zoom player, foobar2000, core media player to view MKv files.
What player are you using?