Tutorial for beginners

Here I will show the basics of video editing for anyone who's just getting started.

What you'll need:
Windows Movie Maker
The video(s) you want to edit, and any pictures or music you want to add
YouTube Downloader, if you don't have any material

First, open up Windows Movie Maker, which should have come with your computer. If not, you can download it here. I recommend version 6.0 because the quality of the finished product is better, but if it's incompatible with your operating system you can get 2.1.

Once you have Movie Maker up, import your video(s) into it by clicking the Import button on the left and finding the files you want to use. It's a good idea store them all in your Videos folder. It will look like this (here you can see material I'm using, lol):

If there's an error, check to see if the file is an .mp4, .flv or QuickTime movie. Windows Movie Maker doesn't accept those formats, so you'll need to use YouTube Downloader to convert them. I recommend the .avi format if you have Windows 7, otherwise the video might not publish.
 
Once you have your media imported, drag what you want to use into the timeline (which you can change to a storyboard, but I find timeline much easier). Once it's in there you can edit it many different ways.

If you just want to use a few small clips of the media, you can split or trim it. The split button is on the far right of the preview window. Using the preview window, find the place you want to cut (you can go frame-by-frame by clicking on the buttons beside the play/pause button) and the click the split button.

You now have more clips to work with.

Trimming is different from splitting. To trim, you take hold of the beginning or end of the clip and drag it. Any part you drag past is removed - but if you shorten the clip by trimming, you can re-extend it to get the material back. You can't extend clips after splitting them, although you can press Ctrl+Z to undo the split (and anything else you do).

There are a variety of effects you can add to your clips as well. Right-click on the clip you want to edit and click Effects, choose what you want to do to it and click Add. You can add up to six effects to each clip.

You can add music or other audio by simply dragging an audio file to the audio track below the video track.

If you want to completely dub over the video clip with the audio, expand the video track by clicking the plus sign to the left of the track, then right-click on the tiny audio track that appears, and click Mute.

You can put captions on your video by clicking "Titles and Credits" to the left, under Edit. Select the type you want to do and write your caption, then click Add Title. You can also change the color, font, size and animation of the text. It will go in the small track under the audio.

Once your video is finished, click This Computer under Publish, or Publish under Finish Video (I think) if you have Windows Movie Maker 2.6. This will turn your project into a video file that you can upload to websites like YouTube and Facebook.

The first time I made a video - a slideshow of screencaps from The Aristocats, which is still up on YouTube - I didn't know I had to publish it first, and I tried to upload the WMM project file to YouTube instead. XD As you can imagine, it didn't work, but I figured out that I needed to publish it.

All in all, video editing is easy once you know how to work with your software and videos. I'm not sure if I've covered everything in this tutorial, but it's just a basic one and I'm sure anyone who reads it will figure it out. :)