Place the slide onto the stage
Turn on the microscope, so light passes through the slide
Select the lowest powered objective lens, which is usually 4x
Look down the eyepiece lens and turn the coarse focus knob, to bring the image roughly in focus
Adjust the fine focussing knob, to bring the image into full focus
To observe the sample with a high magnification, move the objective lenses, so that an objective lens with a higher magnification power clicks into place
After switching to a different objective lens, you can readjust the focus by using the coarse and fine-focussing knob
