Why don't some files play after downloaded?
 

I have downloaded different video files and have found that some types would not play on my windows media player (such as wmv and avi). I don,t even know what wmv or avi stand for. Only been using limewire for a couple of weeks, plus I'm very computer illiterate.
I'm still trying to figure out my printer for crying out loud.
Can somebody give me some help?