Unlike physical pieces of paper, windows can be resized to take up more or less space. They can also be "minimized," where they are temporarily hidden from view, "maximized," where they take up the entire screen, and "closed," where the page and its contents are removed from view. (Recall that "Close" is a command in the File menu). Also, computers are designed only to focus on one window at a time. Unfocused (or unselected) windows will usually have faded colors, whereas the one in focus will have normal colors. This is to ensure that, for example, when you choose "Close" from the File menu, you close the window that you intend to, namely the one in focus.
On computers running the Microsoft Windows operating system, the three buttons for minimizing, maximizing, and closing windows are in the upper-right corner of each window. On computers running Mac OS X, the buttons are in the upper-left corner of each window. Be aware that on Macs, the green "maximize" button does not actually expand the window to occupy the entire screen. Rather, it resizes the window to "fit" whatever the window contains, so there is no blank space surrounding a photograph being viewed, for example.
Some windows, on both operating systems, are missing some of the "size control" buttons. Usually, the "maximize" button will be the one missing because it would not make sense to maximize those windows.
A tab is a relatively new feature introduced to web browsers (Safari, Internet Explorer, Firefox, etc.) to help organize the application when people want to have many web pages open at the same time. Instead of having one window for each different webpage, people can put multiple webpages in the same window by having each webpage be a different tab on that window. At first glance, this feature may seem useless, but its usefulness shows when, for example, you have five different webpages that you want to minimize or close. If they are in different windows, you would have to close each one individually, but if they are five tabs all in the same window, you only have to close one window instead of five.
Examples
The three "size control" buttons on a computer running Mac OS X:
And on a Windows computer:
Different tabs as they appear in the web browser Google Chrome:
Notice how only one tab can be "selected" or "focused" at once (in this case the "New York Times" tab).
Tomorrow: Cut, Copy, and Paste
