The UART labelled Serial is connected to the D0/D1 socket on the Autonomo Grove Shield. (RX = D0, TX = D1)
If you are using any of the variant boards with the additional UARTs, these are also connected as follows:
Serial2: RX = D6, TX = D7 (Available on the Autonomo Grove Shield)
Serial3: RX = D12, TX = D13 (Not available on the Autonomo Grove Shield)
The RX/TX pins of Serial1 are connected to the Bee socket, these are not connected to any of the other headers.