You can stop severe bleeding by raising the damaged body part, pressing hard on the injury and placing one or more compression bandages (tourniquets) on the injury. If you do not have access to a first aid kit you can use a sweater or the like as a compression pressure bandage, and tighten it with another piece of clothing or a belt.
Never put compression bandages on the neck or chest as it may worsen blood circulation and make breathing difficult. Instead, press the bandage lightly against the wound.