Place the microscope slide onto the mechanical stage where the sample on the slide can be seen through the ocular lens. The mechanical stage is the platform right below the objectives. At this point the specimen does not have to be in focus, and it may appear as a blurry blob. This is OK as long as part of the blurry blob can be seen through the ocular lens.
Use the coarse adjustment knob to bring the blurry blob into focus. The coarse adjustment knob is located at the bottom of the microscope arm, just before the microscope base. It will be a a set of two knobs combined into one: a smaller knob on the outside, which is the fine adjustment knob, and a larger ring knob directly against the microscope arm. This larger ring knob is the coarse adjustment knob, which is good for large focus corrections on lower objective powers.
Adjust the light source so the right amount of light passes through the sample and makes the best contrast with the microscope slide background. The light source is usually located on the microscope base, either as a knob on the front of the microscope base, or as a partial knob for turning located on the side of the microscope base.