One of the things that may be confounding you in your first days of being a Mac user is how to quit your applications. With Windows, if you can’t see any application windows it almost always means you’ve quit the application. There are some newer exceptions to this behavior like instant messenging applications that still run in the system tray.

On the Mac, most applications continue to run until you explicitly quit them. You can quit the application by selecting Quit from the application’s menu in the menu bar (to the right of  the Apple Menu) or by holding the Command key while pressing the Q key while the application is the front-most one. You can tell which application is front-most by looking for its name in bold in the menu bar on the top left of your screen.

There are some Mac applications that deviate from this, like iPhoto, but they are almost always single-window applications. The applications that do deviate from this will quit when you close their last or only window.

Below is a quote from Apple’s Human Interface Guidelines that developers use to help design their applications to be consistent with other applications developed by Apple or other third-party developers.

In most cases, applications that are not document-based should quit when the main window is closed. For Example, System Preferences quits if the user closes the window. If an application continues to perform some function when the main window is closed, however, it may be appropriate to leave it running when the main window is closed. For example, iTunes continues to play when the user closes the main window.