Here are the steps for beginners:
Go to YouTube.com and locate the video of choice.
Click on the box that says Share directly underneath the video screen. You should see this pop up:
Highlight the web address in the box that says Link to this Video. Right click your mouse and click copy.
Go to zamzar.com.
You will see this and you need to click on the letters URL.
You will see this on the screen:
You need to right click your mouse and click paste to put the link from YouTube here. Delete one of the http:// if necessary.
Now find mp4 and click on it because that is the format you need your video to be converted to and type in your email address in the next box.
Once you have done all of the above steps, click convert and the file will be sent to your email address (be patient, sometimes it takes a long time to show up).
Once you get the email containing the link that looks like this:
Click on the blue hyperlink that the arrows are pointing to and then click the green box that says "Download Now".
You need to choose Save As and locate (or create) a file to put your videos into. I have them sorted into folders by subject inside a folder entitled 1My Videos (I put the 1 in front of it so that it shows up 1st in my files so that I can locate it as fast as possible so I don't lose my audience if you know what I mean!).
I hope this was detailed enough. If not, please feel free to ask any questions if I can be of any further assistance. It is fairly simple once you have done it a few times and it opens your world (and your students') up to MANY NEW and EXCITING visual learning experiences.