These are test flights to simulate some of the conditions the actual, practical vehicle would experience. The end goal is to create a reusable first stage for the Falcon 9. It would operate similar to the normal Falcon 9 during launch, after it burned through its main propellant store it would separate from the rest of the stack (which would then proceed on ahead as usual) then undertake a short burn with a single engine to decelerate the 1st stage (which, at this stage, carries no upper stages, payload, and is mostly empty of fuel, so it is a much easier task than on the way up) enough to prevent it from breaking apart when it contacts the atmosphere. Then, the 1st stage will reenter (somewhat gently), parachutes will open to slow the atmospheric descent and finally small thrusters will guide the stage to a soft, safe landing (perhaps back at the original launch location, perhaps at some other location downrange).
Later the recovered 1st stage would be refurbished and returned to service as part of another Falcon 9. Done properly this should reduce the cost of launches by about another order of magnitude over the Falcon's already ridiculously low costs.