How do I use an oral syringe to administer treatment?

See below. I assume you mean administering a liquid medication to a child or infant. You fill the syringe with the amount of medication then you squirt the liquid into the side of the mouth of the child a little at a time and let the child swallow it the squirt in a little more till the child takes it all. You can ask the pharmacist if you still have questions.
Watch the dosing. The most important thing when dosing infant's medication is to be attentive to the correct dosing. It is best to measure to the closest ml. If the dose is in "tsp", be aware that 1/2 tsp is 2.5ml, 1 tsp is 5ml, etc. After measuring the correct dose, insert the tip of the syringe into the side of your baby's mouth and instill just a little bit at a time. This reduces the chance of it being spat out.