If your microscope has a mechanical stage, like the one shown at the left, you will use the mechanical adjustment knobs to move the slide right, left, forward, and back.
Mechanical stages are easier to use if you want to scan the whole slide which you will want to do if you want to estimate an egg count.
Start with the lowest power which is usually 10X. Move the stage with the course focus knob to just below the tip of the lens while watching from the side so you don't break the cover slip.
Then, while looking through the eyepiece, focus down until you can clearly see the level of the fluid between the cover slip and slide. This can take some practice. It helps to have the corner of the cover slip in view then focus down a little bit or find a bit of debris and focus on it.
You may need to adjust the amount of light coming through the sample by opening or closing the diaphragm under the stage. You will need more light at the higher power.
Once you are in focus, begin to scan the slide for something interesting. To scan the entire slide start at one corner, move all the way to the other side, adjust to the left or right a little then scan again all the way back to the other end. When you locate an interesting object at the lower power, switch to the 40X lens. Simply rotate the 40X lens into place and it will be positioned over the sample. Switch back to the 10X and look around some more.
Next The results.