People are so afraid to start or even preform CPR on a person. It's better to have tried and failed then to do nothing at all. Even if you know nothing at all someone around will know what to do but is to afraid to step up.
The Basics of CPR
First, ABC Airway, Breathing, Circulation
If someone is talking to you they have an airway and their is nothing blocking their breathing.
If someone is not breathing you are going to check their pulse. No pulse means no blood to their heart. Which means you have to help them by preforming CPR to get blood to their heart.
Put the your keel of your hand in middle of chest. Just remember 30:2. 30 compressions on their chest to 2 breaths. Push hard and Fast. If you are to scared to put your mouth on someone, don't do it. It's better to do just compressions on the chest then to do nothing. Also just think, how many people have you kissed or shared drinks with.