Describe how to use an oil immersion lens. Include any preparation and post observing steps

Before even using oil immersion lens, make sure you set the microscope to the lowest objective 4x.

You want to start small before increasing the magnification. Before you move to the next power (from 4x to 10x), make sure your center is focused using the coarse adjustment. Then move to 10x, and do the same adjustment. Then onto 40x, and once you get to 100x, use the fine focus (not coarse focus! because it will move the speciman a lot which messes up your field of view. Fine focus is just refinning so the picture appears clear.

Now, when performing oil immersion, get a dropper, and carefully drop an oil on the speciman, and get a slider to cover on top of it (BUT DO IT SLOWLY! you don't want to get any bubbles in it).