Sometimes wild animals need medication to help them get better.
There are laws in place that mean you have to be a Registered Veterinary Nurse or a qualified Veterinary Surgeon to be able to give medication in certain ways.
A 'lay person' is someone who is unqualified. Under veterinary direction a lay person can give medication orally (into the mouth) and by subcutaneous injection (an injection just under the skin). However, they can't give injections into the muscle or into the vein! This is because the body is a complicated thing and the chances of things going wrong is increased, so it can only be done by qualified people.
Medications must always be given in accordance with the vets directions.