The hotter the chilli, the higher the capsaicin content. Chillies can be eaten raw or cooked or in chilli sauce. Be careful not to eat very hot chillies inadvertently, as you will definitely regret it.
Chillies contain capsaicin, which is the source of the chilli's heat. They are mostly concentrated in the seeds and ribs. Chillies can burn your mouth and stomach, so it is not wise to eat too much of them, as constant irritation of the stomach may increase your risk of developing stomach cancer.