This circuit represents a half wave rectifier of an AC signal. It allows current to flow only in the positive half of the sine wave. In the positive half of the sinusoidal waveform the diode is forward biased and a forward current (Id) will flow. The load voltage is equal to that of the source minus the drop on the diode (here 815mv). As for the negative half, the diode is reverse biased and a negligible current (reverse saturation current Io) will pass. The circuit is considered to be open and the load voltage to be zero. The frequency of the output signal is the same as that of the input signal.
