Microscopes are much like cars in that you can spend a lot of money or a little, or buy something merely functional or expensively appointed. Whether the microscope is new or used doesn't really matter, so long as the microscope works. For these techniques, you can use a microscope that has a built-in light source (battery or electric), or uses a mirror to reflect ambient or natural light. The objectives can be interchangeable, or set for that particular microscope by the manufacturer. You can purchase prepared slides or prepare your own. If you want to make your own slides, you will need plain slides, cavity slides and cover slips.
When preparing a slide, you'll need to know first what you will be examining. Different techniques are used depending on the specimen, both in preparation and in viewing. If you will be viewing gross anatomy or surfaces, such as examining a leaf, your light source should be shining down onto the viewing field, and your specimen should be placed on a plain slide; if the specimen is small, you may want to add a cover slip. If you will be using oil to assist in the viewing, a cover slip is required. If you will be viewing microorganisms especially in water droplets, your light source should be shining up onto the viewing field, you should use a cavity slide and a cover slip. For prepared slides, your light source should be shining up onto the viewing field. If you are using a microscope for a class assignment or as part of your work, your teacher or supervisor will tell you what types of slides to prepare. The complexities of staining and preparing individual specimens are beyond an article of this scope.
Once the slide is on the microscope stage, choose the lowest objective. Using the gross or coarse adjustment knob, focus on the slide as you look through the eyepiece. Make whatever notations you need to record what you have observed. Next move to the next higher objective, and use the fine adjustment knob for focus. Again, record your observations. Finally, move to the highest objective, and use the fine adjustment knob for focus. Record your final observations. Certain objectives require you to place a drop of oil on the cover slip; do so if and when indicated by your objective.