When showing someone how something is done in Windows, you usually either use your small mouse cursor or your fingers to point the things out to them. But a better way would be to use something like a marker pen which can easily highlight what you are trying to say to the learners. I do not suggest you to use the marker pen on your computer screen, but you can use the freeware Epic Pen software instead. It is a software using which you can draw over your desktop in many different colors. The drawing stays over the top of all the applications and therefore makes it very useful application for demonstration purposes.
You can download Epic Pen from the sourceforge website. The download is available as a setup installer. The download is a little around 1 megabytes in size. After the installation, it adds a new shortcut in your Start menu using which you can run it. The application shows a tiny panel on your desktop containing color selector, pen tip width selector and selector for pen or eraser.
You can select the pen tool from this tiny panel, choose a color and start drawing anything on your desktop. If you draw something and want to erase it, then you can use the selective eraser tool to erase portions of the drawing. If you want to erase everything, then you can use to full eraser tool. There is an option to hide/show the ink if you want to hide the drawing temporarily.
Epic Pen is a very simple drawing application which can be used to demonstrate the people how to do something on your computer. It has very easy to use Microsoft Paint like tool panel to select the colors and other tools. It also supports hotkeys for easily selecting the tools from the panel or hiding/showing the ink (drawing) on your desktop.
You can download Epic Pen from http://sourceforge.net/projects/epicpen/.