How to Split Screens on a Macbook
With the Apple OS X operating system, any Mac computer screen can be split across two monitors. The MacBook will automatically detect the second monitor and configure itself for the optimal resolution. By default, the second monitor will display the same screen as the MacBook's display. You can use system preferences to change this to a split-screen view and then arrange the two displays to the way you want them.
Examine the end of the monitor cable to see if it will fit in the min-DVI adapter on the MacBook. If it does not, you will need to attach an adapter to the cable.
Shut down the MacBook. Turn off the exterior monitor. Connect the monitor cable or adapter to the DVI port on the side of the MacBook.
Turn on the MacBook and the monitor. Wait for the monitor and the MacBook display to power up. The image on the monitor will be the same as the image on the MacBook display. This is called a mirrored display.
Click the "Apple" menu at the top of the screen. Select "System Preferences." Select "Displays" in the "Hardware" section.
Click the "Arrangement" tab. Both displays will be shown in the preview pane of the window. Deselect "Mirror Displays" by clicking the check-marked box. This will put the displays into split-screen mode.
Drag the screens in the preview pane with the mouse to change their positions. For example, you can have the exterior monitor to the left or right of the MacBook display or above or below it.
Close the Display Preferences window to automatically save the display settings.