CNA stands for Certified Nursing Assistant, Nurse Aide or Nurse's Assistant, and just as its name implies, a CNA is a trained professional who is basically an assistant to Licensed Practical Nurses (LPNs) and Registered Nurses (RNs).
A CNA’s role vary depending on the setting – hospitals, nursing homes, and other facilities that offer long-term care - s/he chooses to work in. For example, responsibilities of CNAs working in nursing homes are a bit different than those working in public hospitals.
In any case, as a CNA, you will be responsible for assisting LPNs and RNs with the basic care of patients. You will also be responsible for relaying essential information to nurses in charge pertaining to such things as changes in patients' behavior and/or condition. You will have direct, daily contact with patients as you help them with their daily activities.