On the top half of the microscope, three parts contribute to your view of the objects it will magnify. The eyepiece is where you place your eye to see the image of the object. The body tube extends from the eyepiece to a rotating nosepiece containing the objective lenses, which determine the amount of magnification used to show the object.
The arm of the microscope -- the large space between the nosepiece and adjustment knobs with which you can carry the microscope -- serves as the microscope's body. Underneath the arm, sit two knobs. The larger coarse-adjustment knob can make drastic focus changes by moving the stage or the upper part of the microscope, while the fine-adjustment knob lets you fine-tune the focus.
The stage is the platform on which you will place object you'd like to magnify. Two stage clips keep objects gripped tightly onto the stage. You insert a slide underneath the stage clips and push it to the back of the clips to view the slide through the eyepiece.
The aperture -- the hole in the middle of the stage between the two clips -- allows the light to shine through the slide. Underneath the aperture, a light or mirror makes the object visible through the eyepiece. The diaphragm, a sliding circular tool that adjusts the amount of light let through the aperture, allows you to brighten the view of the object when you look through the eyepiece.