how to open a .wmv file

A .wmv file is a windows format. To open one you need a tool such as FlipForMac, you can find it by using Google.

If you only need playback, VLC will play .wmv videos.

If you decide on Flip4Mac, get it ONLY from the developers site:

http://www.telestream.net/flip4mac/overview.htm

I see it offered free on other sites but those sites have a reputation for "Free" meaning they load you up with malware that will make your Mac run poorly.

Flip4Mac is payware but well worth the small expense.