When a program needs information from you, it may create a temporary pop-up window, known as a dialog box, instead of displaying your options in the main program window. While every dialog box differs, almost all have two main ways you can close them: by inputting information and confirming it or by cancelling the process.
Applying Your Changes
After entering whatever information a dialog box requests, click "OK" to close the box. Some dialog boxes also offer an "Apply" button. Pressing this button applies the changes you entered without closing the box, allowing you to test their results. "OK" automatically applies changes, so you don't need to click "Apply" before pressing "OK" every time. You can also select "OK" by pressing "Enter" on the keyboard in most boxes.
Cancelling a Dialog Box
Clicking "Cancel" on a dialog box will discard any changes made in the box. In applicable cases, cancelling the dialog box will also cancel whatever action you selected that opened the box. Most dialog boxes also display the standard "X" in the corner to close the window. Closing the box this way works the same as pressing "Cancel." In some programs, you can also press "Esc" to cancel input.
Some dialog boxes use terms other than "OK" and "Cancel." For example, when opening a file, the buttons will read "Open" and "Cancel." In this case, "Open" performs the same function as "OK," using your selection and closing the box.
Hidden Dialog Boxes
If you can't see or can't access the dialog box you need to close, try holding "Alt" and pressing "Tab" repeatedly to cycle through all open windows. This key combination can bring up a dialog box that gets stuck behind other windows. If the dialog box's title appears on the Windows taskbar, you can also try right-clicking it and choosing "Close Window."