What do you mean by "two separate monitors"? Typically, one can run in
"Clone Mode", where the monitors show identical content, or "Extended
Mode", where the two monitors logically form a single display and you
can travel with your mouse from one to the other as if it was a
continuous large monitor. True, in Extended Mode it is possible to
arrange one's various windows so that functioally they can be thought
of as "two separate monitors".

Anyway, not all graphics cards support all modes. It should be possible
to select the desired configuration from the graphics driver's user
interface, which would hang off Display Settings (right clock on the
desktop > properties > settings > Advanced, and you should see a tab
for your graphics controller). It is also possible to use Window's
controls (right clock on the desktop > properties > settings) by
clicking on the appropriate monitor in the shown box in conjunction
with selecting or deselecting "Extend my monitor..." option. I've found
that it is better to use the graphics controller interface, as it
sometimes reflects more accurately the hardware's capabilities.