I often run a lot of windows at once-- even 50, 60, 80 windows. If you use the toolbar, connected to the start button at the bottom or side of your screen (wherever you've put it) and you have, say 33 firefox or internet explorer windows open, like I do now, it can be a pain to go from one window to the next.
Or let's say you are on an internet site and want to selectively copy some information from parts of one web page or from several web pages, to one MS WORD or text file page. It could be a real hassle to switch back and forth if you have to use the icons on the open windows tool bar.
There's an easier way.
Press on the "alt" key, and then, gently tap the tab key. If you let go of both keys, you'll return to the window you were on before the current page.
Once you get in the habit, this is a really fast, handy way to switch between two open windows.
If you continue to hold down the "alt" key, you'll see, at the bottom of the dialogue box that appears, the text which describes the next page icon that appears along with about 20 of the previous pages you've been on. You can tab from one to the next to more easily see the contents of the other windows you have open.