You need to add the appropriate actions to a VoiceAttack command, just as you would otherwise.
The example consists of a "Loop Start" action (with its matching "Loop End" action, which is added automatically with the former), containing a "Begin a Conditional (If Statement) Block" action (also with its matching "End a Conditional Block", again added automatically).
The "Write a Value to the Event Log" action within the condition is to illustrate where the actions you want to execute if the condition is met (I.E. Right Shift and Joystick 1 Button 3 are pressed simultaneously) should go.