[virtuald]

Create an object, call Set() on it.

// some global somewhere... 
Jaguar my_motor(2);

.. 

// in your main loop
my_motor.Set( 1.0 );  // full speed in one direction
my_motor.Set( -1.0 ); // full speed in another direction

However, I suspect that is not what you're asking. If you want to control the motor using some external input, then the easiest thing is just pass the value retrieved from a joystick.

// some global somewhere
Joystick stick;

... 

// in your main loop
my_motor.Set( stick.GetY() );