Some liquids can be mixed with food. If you do this, make sure that the cat has eaten all of the medication. It is best to give the liquid medication in a small amount of food and only give the remainder if the cat has eaten all the food with the drug in it.
If your cat will not eat its food with the medication mixed in, you can apply the drug directly into the mouth of your cat. To do this, the easiest way is to use a syringe, which you can get from the vet. Draw up the required dose from the bottle, approach your cat from behind, gently hold your cats head around the tops of the ears and place the nozzle of the syringe in between the lips of the cat from the side while holding the cat's head steady and slightly lifted upwards. Gently squirt the medication into the mouth and if necessary rub the cat's throat to induce swallowing. Have someone help you if the cat does not hold its head still.