1. Find free on-line cutter website called : ytcutter.com. You can only cut the time of video: 1 minute for free of charge to use this website.
2. open your favor youtube video, copy URL and paste address into the box of Paste youtube video URL and click start
3. The screen will show youtube for you to review. While video is running at the time you like to START
then, click "start" button: running at the time that you want to end, then click "end" button
4. click "preview" of your cut video to review to your desire.
5. click "download" (it will goes to MP4 format file) to save the file in your PC.
My original youtube video: https://www.youtube.com/watch? v=50nq_SLAYD4
My cutting youtube video: