Use the Dock
The Dock is that strip of icons across the bottom of the screen. The specific icons that appear in the Dock will change as you open and close applications, view photos, or customize what's in it yourself. Hover your mouse over an icon to see a label appear that tells you the name of the application or file.
To open an application or document from the Dock, single-click its icon.
The tiny black triangle underneath an icon indicates that particular application is open and available. Even if you don't see it on your screen, you can single-click the Dock icon and that application will come forward, ready for you to work in. Keep an eye on the application menu (as described on page 30) to verify which application is “active” at any moment. ...