Take a clip and put it into the Timeline. It is better to use the Timeline view in your Windows Movie Maker project for this purpose. When it is in there, play through the clip to find the places you would want to cut out. Go and put the cursor either on the beginning or end of the clip depending on what you want to cut out.
You will notice that the cursor becomes a red doublesided arrow, and there will be a message that reads “Click and drag to trim the clip.” Now just click down, and start moving toward the center of the clip. This will begin shortening the clip from the beginning or end of the clip, cutting off all that you moved in from. This will not affect the clip as it sits in the Collections, just what is in the Timeline. If you do not like what you just did, you can press down again and stretch it back to its original position.