Typical beginner circuit. It is better to have buttons connect to ground and use resistors to pull to 5V. In the arduino these are even fitted inside the chip and can be activated by a digital write high to the pin once it has been set as an input.
Why are the outputs labeled A0 to A5, these are analogue INPUTS in the arduino world, although these pins can be used as outputs but treat them as pins 14 for A0 , 15 fro A1 and so on.