I work as a lifegaurd on the beach. 
what are the main responsibilities of a lifeguard?
We are responsible for the safety of people in an area of water. We need to ensure that there is no harm of beach goers. 
are you a lifwguard at a pool or a beach?
At a beach, although I do sometimes lifegaurd at pools. 
I understand lifeguards have to be trained in cpr, have you had that training
That is correct. It's is a very important part of becoming a lifeguard. You need to be certified before becoming one.
I have heard that in some areas lifeguards are part of the emergency rescue teams, have you done that