CPR involves chest compressions and rescue breathing as per the American Heart Association guidelines. Currently they are saying that the compressions are more important than the breathing.
An AED is an Automatic External Defibrillator. These are usually located in public areas in the event that someone experiences cardiac arrest. When you open the box, you would turn it on and it will tell you everything to do. Basically you attach the pads to the patient as per the pictures and then stand back and allow the machine to read the cardiac rhythm. It will tell you if a shock is needed and which button to push to do this.
Hopefully you will never have to worry about it, but its good to always know.

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