D620 latitudes using a Dell docking station with Dell monitor

D620 latitudes using a Dell docking station with Dell monitor. Trying to configure
the laptop to extend the desktop from laptop to my DELL LCD. My primary is monitor one , what will my monitor 2 be setup to to have the desktop extend to it and still keep the laptop monitor accessible for doing something else.

In other words,
Want to configure one to be the primary and extend the desktop to the second one.

Thanks!