Ionic wind, or coronal wind is simply air flow produced by electric charge. Like any thruster lift can be produced if the flow of air is in the downward direction. Newton's Third Law states that for every action there is an equal and opposite reaction. A force exerted to push air down results in an equal and opposite force on the object producing the thrust. A jet, a fan, or a rocket all produce thrust by directing a stream of air or gas in the direction opposite to which you require the craft to move.
A good description of coronal discharge and ion winds can be found here: IonWind.