Instructions
Launch "World of Warcraft," then log in using your user name and password.
Choose a character from the character selection screen.
Press "Escape" on the keyboard, then click "Macros" from the listed menu options.
Click the "New" button located at the bottom of the "Macro" interface.
Enter a name for the macro in the "Name" dialog box, then click an icon to represent the macro.
Click "OK."
Click the "Edit" button.
Enter the random cast macro command into the text box. The format for the random cast macro is "/castrandom" followed by the ability or spell names you want the macro to choose from (i.e. "/castrandom frostbolt, firebolt, lightingbolt). You can enter as many spell or abilities as you want.
Click and drag the macro icon to a empty slot on your ability bar, then close the macro window. The random cast macro is now ready for use.