Visit a local software retail store and browse their collection. One advantage of CDs is that they are intended for people to use on their own publications. It's wise to check the license agreement though, just to make sure publication on the Web is allowed. I suspect that you will get better results saving a graphic image as discussed in the From the Web section, because every time an image is rendered on screen and re-captured as a file, some of the original quality may be lost. The quality is limited by the resolution and color depth of the video display you are using when you do the capture, and that may be lower than the quality of the original.
Screen captures are useful for illustrating computer processes - showing menus and buttons.
I do it frequently in preparing lessons, but that's a bit specialized. The most convenient way to do this is with a graphics program such as PaintShop that lets you select the area of screen you want. You can then fiddle with it if you like, or save it directly in a Web format. Most scanners look like small photocopiers attached to computers. We can't go into detail of how to use a scanner in this module, but it's not hard.