this is what my dummies book says:
The longer you use wijdowsk the more likely you are to want to see two windows side by side. For example, you may want to copy and paste text from one document nto another document. By spending a few hours with the mouse, you can drag and drop the windows' corners until they're in perfect juxtaposition.
Or you can simply right click on a blank part of the taskbar (even the clock will do) and choose Show Windows Side by Side to place the windows next to each other, like pillars. Choose Show Windows Stacked to align them in horizontal rows. (If you have more than three open windows, Show Windows Stacked tiles them across your screen, handy for seeing just a bit of each one)
If you have more than two windows open, minimize the ones you don't want tiled. Then use the Show Windows Side by Side command to align the two remaining windows.