In Pictures: 10 things every new Mac user should k...
Just quit already
Unlike a PC, where you click the X in the right corner of your screen to close a program, the Mac's left-sided red dot only closes the window, leaving the application still running. In order to avoid using precious memory, when you want to quit an application, look for the bolded text in the menu bar with the application name. Click the name and then click Quit; alternatively, a quick ⌘Command-Q will also do the trick, as will right-clicking on the icon at the bottom of the screen and selecting Quit.
In Pictures: 10 things every new Mac user should know