There is a green LED to indicate the presence of power, and an ON / OFF latching switch to control the power to the board. On this particular model and version, the center pin of the barrel socket is positive; however, please double check with the manufacturer’s instructions, in case they have made any changes. You have to push the switch IN to use this device.
The operating instructions state that the input voltage through the barrel socket must be between 6.5 V and 12 V. Hence, if you wish to use it to its maximum capability you will need to remain in that range. This is a non-adjustable fixed power supply model, which is good enough for most applications. The manual states maximum output current to be 700 mA. However, it is probably better to use much lower voltages and current to be on the safe side in case you make a mistake on your breadboard circuit.