There are two copies of the board, front and back.  The Nano is soldered directly for the top side of the front board.  Header sockets are also soldered to the front side and the LCD shield is inserted into them, over the Nano.

The RTC and buzzer are soldered directly to the underside of the front board, along with the connecting header.

The back board top side has the SPL06 and the connecting socket strip

The underside has the two push-buttons and the slider switch, plus the power connector.

The two boards are joined by the header/socket strip and supported with standoffs.