CPR stands for cardiopulmonary resuscitation. It is an emergency life saving procedure that is performed when someones heartbeat or own breathing has stopped.
Nobody ever knows when they are going to be confronted with somebody not being able to breath, which is why CPR is important and which is also why it saves lives.
When somebody goes into cardiac arrest CPR can be used to keep a person alive until the paramedics arrive, but without anybody knowing CPR there is a possibiltity that the person could become brain damaged or even die. Within eight minutes of losing oxygen in the blood the brain starts to become brain damaged so it is important that the procedure is performed immediately. There have been many cases where people have died when simple CPR could have been performed to keep them alive.
The British Red Cross offers CPR and life saving courses. The website also shows you videos and teaches you how to carry out CPR. Learning CPR is important because you never know when you might need to know it.