CamStudioThis is a free software package that works very well. You can download it from http://camstudio.org (they request a donation only - a very good deal).
I find it does a great job with sound recording and screen capture. It is a little bit clumsy to use, but just to get the main ideas onto the screen is pretty simple. Essentially, I just record what I want to do on the computer and talk as I do it. I take the finished file, and put it into YouTube. You can also create a shockwave (Flash) version, but these do not play on iOS devices (iPhone/iPad).