Depends where you live.
I haven't really seen hospitals utilize CNA's (or STNA's here in OH) in my area - they will hire those with an STNA certification already, but generally they are just called nursing assistants. At my old job, we were called PCNA's (patient care nursing assistants).
When I was a PCNA, I could do basic patient care, I/O's, admit pts on tele and hook up all of their wires/etc, get blood sugars, and d/c IV's/foleys and do simple (non-sterile) dressing changes. The nursing assistants at my current job can only do basic patient care, I/O's and if you're in the critical care or telemetry units, you can admit pts on tele.
Patient Care Techs (PCT's) at my old job could do everything a PCNA could do + do blood draws and insert foleys.
I am a nursing student technician (NST). To be an NST at my hospital, you have to be in nursing school with at least 1 year of experience. They pretty much let me do everything except pass meds and do assessments, although there is sort of a gray area with assessments because we are allowed to do dressing changes (both sterile and non-sterile) and you have to assess the wound bed. I can draw blood, insert IV's, insert foleys, administer enemas, do blood/wound cultures...in critical care units, they have me prime and hang tube feeing bags in the morning and I'm also allowed to suction patients with trachs or vents if they need to be suctioned. I truely love my job because it is such a wonderful experience.