Nikon D3100? How to use?

So I got a Nikon D3100, and I make youtube videos. So i checked it out at sears and it had really good quality anyways. I made a video and I can't edit it with windows movie maker. Because it doesn't support it.
What free software can I use for it?

Added (1). I didn't buy it just to make videos.
I take photography classes and I have to take pictures for weddings and festivals this summer.

I do have another camera… An actual one that is set for recording, but the quality isn't too good. And since I'm now partnered with youtube i need good quality videos! (HD)

OK I'm gonna be honest with you, ok? Do not even think about shooting someone's wedding if you are not fully in control of your camera and aware of the situation. You can easily get sued for ruining someone's special day (and even end up in jail, so yeah it's not that easy. This is why wedding photographers carry back-up bodies, lenses, strobes and speedlights, batteries, memories, etc because if you ruin it in every size and form and shape, you are going to become miserable and I'm not exaggerating at all.)

What is your question here? How to use the D3100 or how to edit the videos? There are tons of videos on YT on how to use the D3100. Jared Polin (FroKnowsPhoto.com) has great videos on D3100. Check them out.

For editing your videos, you need a fast computer because 1080p Full-HD videos are very big in size and need a lot processing. I don't really know a good FREE video editing software because I'm not a videographer but I know about Final Cut Pro, Sony Vegas and Premiere Pro. They are super-powerful programs that all videographer have to know about but they are not free.

Why did you buy a still-image camera for recording videos? That's like buying a Corvette to tow a camper - yes, it will get the job done, buy why not buy proper equipment?

Nikon thoughtfully provided a user's manual with your camera. The videos should be upload-able to WMM…

You are going to shoot weddings and you are asking how to use your camera?

Point and shoot.

If you need info on how to use your camera, I think you should check out this great DVD from Quickpro they take you beyond the words of the manual and show you how to use your camera and get the best pictures you can with settings and adjustments.
http://www.quickprocameraguides.com/p.Nikon.D3100.html