What are the Alt (Option) and Control (Ctrl) keys for?
Answer: These keys on the keyboard are called "modifier keys." They are typically used in conjunction with another key on the keyboard to perform a specific function. For example, in Windows, Alt-F4 (press and hold Alt, then press F4) is often a shortcut to close the active window. Control-C is usually a shortcut to copy selected text or a selected object. Control-V is the shortcut for pasting the copied data.
On the Macintosh, the Command (or Apple) key typically has the same function as the Control key in Windows. The Control key on the Mac can be pressed while clicking the mouse button to perform a right-click. Many programs on both Macs and PCs use mutliple modifier keys for shortcuts for certain operations. For example, to save an image for the Web in Photoshop, you can press Ctrl-Alt-Shift-S in Windows or Command-Option-Shift-S on the Mac.