Well first BSI (basic substance isolation) then , you have to check ABC ( airway, breathing circulation)...
Clear the airway, jaw trust (if trauma) or head tilt , chin lift (if no trauma)
Then feel and listen for breathing and look for raising of chest or not
At that point if no breathing, 2 rescue breath....look for chest raising ...
Take pulse (carotide), if no pulse iniate CPR....
30:2 for 1 rescuer, 5 cycles and then reassess....
That s for basic first responder....
If you have an AED then after you determinate the patient isnt breathing and doesnt have any pulse you just should put the pads on and follow instructions
It will tell you if shock advise or not, will tell you to stop CPR or to iniate CPR...
AED are now all bipole...meaning the electricity is going from 1 pad to the other and then back to first pad....
The AED will only shock basic disrythmyas.....meaning that if you do have a complex heart rythm ( blocks....) it wont shock....
you can look on that site >>>
http://depts.washington.edu/learncpr/