In the circuit, for two inputs A and B, output is shown. The circuit will indicate

If any of input A and B is zero, then the diode connected with that input will be in forward bias. So it will behave like a short circuit, so output will be zero.
If both A and B input are 1 (+5 volt) then any of the diode will not conduct current
so $i\to 0$ , so p.d., across the resistor
$iR\to 0$  so output voltage will be +5 volt (high).