First of all, your Go Pro is a camera, not a video file. We should shy away for substituting "MP4" with "Go Pro" in order to keep everyone in the loop.
Next, Windows Movie Maker is awful and I don't think you can import MP4 into it. Converting to a different format just for that would be a huge pain in the ass for no return. Use Google and find out how to get Adobe Premier or Sony Vegas to start learning. Anyone can do it, you just have to mess around to get the basics until you get hung up on something more difficult.
I don't know if that answers all your questions or not, but hopefully it helped some.
PS - If people want to hate, your pleas for civility aren't going to stop anything. Just ask your question like an adult and sift through anything that isn't helpful. No big deal.
"For me, my family, my friends and skiing, that is for me. That's my life. The joy I get from skiing... that's worth dying for." - CR Johnson