Are you talking about typing Arabic? If so, you just go to system preferences/languge & text/input sources and check the box for Arabic, plus the box for Show Input Menu in Menu Bar, plus the box for Keyboard Viewer. Then you select Arabic in the "flag" menu at the top right of the screen and type. Select Keyboard Viewer from the same menu to see which key does what.
For typing Arabic, Mellel is the best app. TextEdit, Nisus Writer, and OpenOffice should also work OK. MS Word does not support Arabic at all and Apple Pages has bugs.
If any further questions, just ask again.