To create stereoscopy in MiddleVR you will most of the time use a stereoscopic camera, then associate this camera with a viewport. The stereoscopic options are chosen in the viewport parameters.
There are several ways to display stereoscopic images in MiddleVR :
Active stereoscopy means displaying the left and right images alternatively on the screen. You then need glasses that will hide the left eye when the right picture is visible, then switch: when the left picture is displayed, hide the right eye. Those glasses have electronic shutters to achieve this, which is why they are called active glasses, which also gives the name to active stereoscopy.
The active stereo mode, also known as the OpenGL quad-buffer mode, requires specific graphics card, typically professional cards such as NVidia Quadro cards or ATI FireGL pro cards.
You also have to active this mode in your graphics drivers. Refer to your drivers manual to find out how.
Passive sterescopy is often achieved by displaying the left and right images side by side or at least displaying the two images at the same time. You then have to put "passive" glasses, which don't have any electronics, which can achieve the separation between the two pictures by means of optical filters, which are often simply polarized filters.