In the first hour, professional help is not there yet. The people who are there are the ones who were already there.
Look after yourself first, and this is not selfishness. A person who becomes a second casualty has doubled the work of the people coming to help. Do not enter water, smoke, a damaged building or a road to reach somebody. If you cannot reach them safely, note exactly where they are and tell the emergency services.
What actually helps, without training.
- Call emergency services and say clearly where before anything else. Location first: everything else can be asked.
- Severe bleeding: firm, continuous pressure directly on the wound, with whatever cloth is to hand, and do not lift it to look.
- Someone unconscious but breathing: on their side, airway clear, stay with them.
- Someone cold, wet or in shock: get them dry, off the ground and covered.
The thing that helps most is staying. People who are hurt and alone deteriorate faster. Somebody sitting with them, saying what is happening, is doing something real.
This is what a bystander can usefully do while help is coming. It is not medical training and no course on this site is.