HELP!!

Dear Internet Followers,
I am in need of your expertise. Last night I filmed Natalie's first guitar lesson with hubby's camcorder - which I have never used before. To my dismay, I came home and found that everything recorded in a MP4 format and my Windows Movie Maker gives me an error every time I attempt to use it to edit this format. I tried some other program I found online that converts any format to any format - the only problem is that it too gave me an error, and I am at a loss. I don't know what to do! I want to edit the video so I can post tidbits of the class online, but I don't know how. Can anyone offer some advice or program to use?