When a person is unconscious their muscles relax and their tongue can block their airway so they can no longer breathe. Tilting their head back opens the airway by pulling the tongue forward.
Should I try to talk with the person? Yes, talk to the person and reassure them. Even though they might not respond to you, they may still be able to hear what is going on.
What should I do if someone is feeling faint? If someone is feeling faint, advise them to lie down on their back and raise their legs to improve blood flow to the brain