What is the technical role of a flight attendant?
I flew for a major airline as a flight attendant for 7 years.  The FAA requires flight attendants on board for the safety aspect of passenger service and sets the minimum number based on the aircraft's passenger capacity.  We usually flew with at least one more crew member than the minimum required by the FAA.

Our FAA mandated duties include safe boarding, including stowage of personal articles, arming the evacuation slides after the doors are closed, a safety briefing prior to departure, verification that the cabin is safe for flight, inflight enforcement of pilot instructions (usually return to seats and fasten seat belts), and to render passenger assistance as necessary for flight safety.  Same for pre-landing and de-planing.  First aid training (including how to deliver a baby in-flight) was rarely seen by the public.  

Annually we would be required to attend jet recurrent training where we reviewed NTSB accident reports with an emphasis on cabin crew responses to emergencies, review of first aid and CPR techniques, re-testing of our knowledge of the location and how to use all the safety equipment on board, including life preservers, life rafts, and emergency slide procedures.  We were also briefed on any changes to FAA mandated procedures and tested on everything.  

We were trained to be current on every aircraft the company flew so that we had maximum flexibility for our scheduling.  At the time I flew, this would have been B-727, B-707,B-757, B-767, DC-9, DC-9 stretch, and L-1011.  That meant we had to know the location of every flashlight, first aid kit, supplemental oxygen bottle, safety briefing kit, life raft, life preserver, safety exit, safety lighting, etc. for every aircraft type we flew.  

The normal passenger service duties that passengers see such as food and beverage services, in-flight entertainment and generally trying to be accommodating, were in addition to the FAA required duties and were entirely up to the company's discretion to provide and train us for.

The FAA mandated safety aspects of flight attendant duties have become so integrated with the normal flow of a commercial flight they can go nearly unnoticed, especially for routine travelers.

And no, we weren't trained how to land a plane in case all the pilots got sick at the same time and passed out.