CPR involves three steps: circulation, airway, and breathing (CAB). For adults, circulation involves 30 chest compressions at 100 compressions per minute, followed by two rescue breaths. This one cycle should be performed for two minutes before calling emergency services. For children ages 1 to 8, use a similar procedure but with only one hand for compressions. For infants, gently compress the chest with two fingers at a rate of 100 times per minute, tipping the head back to check the airway after 30 compressions and providing two gentle mouth puffs of air if not breathing. Continue CPR for two minutes before calling for help.