Answer:
Keep in mind this changes from microscope to microscope.
Step-by-step explanation:
On most classroom microscopes, there will be two knobs on either side of the scope. These will increase or decrease the height of the "stage", which is how you "focus" the microscope. The larger knob will move the stage the most, and thus, is called the coarse focus. The smaller knob is called the fine focus, and, you guessed it, will move the stage the least. There are usually three "objective lenses". Each will have a different magnification and will be listed on the lens itself. It rotates around the "revolving nosepiece". MAKE SURE THAT THE SLIDE IS LOWERED BEFORE ROTATING THE LENSES!!!! If you don't you WILL break the slide and you WILL get death looks from the teacher.
On the stage, there are two clips. They move NOT up and down, but they spin. what you want to do is to move the slide into the clips. They will not break if you do not bend them more than what the slide will bend them to.
The technique for focusing the microscope is really easy once you do it a few times. After making sure that the microscope is plugged in and the light on and the slide and lens in the lowest position/magnification (!) move the coarse focus knob so that the object in the slide is just visible. Once you do that, from there use the fine focus knob to make the object most visible.
These instructions vary slightly from model to model of microscope, but the picture below is very accurate and everything I warned you about is for all microscopes.