Quit Application Gotcha
In Windows to dismiss a window you can click on the X in the upper right of the window. As explained in a previous post, there is an equivalent on the Mac, the red circle with an x in the upple left. But there is a small gotcha difference. In Windows, if it is the main application window that you close by clicking on the X it also quits the application. However, on the Mac with a few exceptions (System Preferences, Dictionary, and Calculator) the window will close but the application will continue to run. This is not a big deal but it will eat up some of your memory and may lead to unexplained behaviour.
To really quit the appication, use the Quit command in the Menu Bar under the application name, the keyboard shortcut command-Q, or right (control) click on the icon in the dock and select Quit.