The first option you have in case you have a monocular or a binocular microscope, is to mount the Moticam onto the eyepiece with the included eyepiece coupler that comes included in your Moticam box.
The other choice is to mount it into the eyetube, with a B&S adapter kit. It has to be placed instead of the eyepiece and fits into the eyetubes of several diameters.
The C-mount adapter allows you to attach your camera to the trinocular port of your microscope, combining optical and mechanical tasks. The adapter has to be chosen in relation to the chip size of your camera, and it is Brand and model specific. It has to be bought to your microscope supplier. Depending on the area of the FOV you wish to capture, you can choose among different magnification factors: 1X, 0.65X, 0.5X or 0.35X.
Know more about the importance of selecting the right C-mount adapter here