In some of Apple’s own apps, like those in the iWork or iLife suites, a separate pop-out window is used to let you view and change settings. This is called the inspector, and usually appears on either the Command+I or Option+Command+I keystrokes.
What’s not obvious is that you can have two or more inspector windows visible at any given moment. Just hold down Option and click one of the icons in the inspector’s tab bar. See below for an example taken from the Pages word processor, which is part of iWork.
Although Microsoft Word has something similar in its Toolbox window, this trick doesn’t work there, unfortunately.