First Aid is what you can do to assist an injured person at the scene using only what is available under the prevailing circumstances. You may only have your two hands, remember that first aid does not rely on equipment. In some circumstances if there is nothing, or nothing more can be done, then first aid may mean going for assistance. The patient relies on you. In practical first aid, especially in the bush, clear logical thinking and the ability to improvise are critical aspects.
First Aid is based on commonsense, knowledge, and technique. The order of urgency is protection of the patient from further injury; ensuring those giving aide are also safe from injury; and the restoration of breathing and heart beat. After this, you can attend to stop bleeding, minimise pain, reassure the patient, seek further aid and if necessary transport the person to hospital. Before you can commence rational treatment a diagnosis must be made consisting of History - the story of how the injury occurred, Symptoms - what the patient feels; Signs - what you can observe.