The questions are:
1.Along the signal pin from the Arduino, there are those other 2 pins for supplying. What should I do with them? Connect them to the Arduino? Leave them alone?
2.What should be the voltage for the signal pin coming from Arduino? (I have a 3S battery for the motors, and a 2S battery for the platform)
1. connect signal and at least one ground (if you have multiple ESC). The supply line is unconnected, assuming you are powering the arduino separately.
2. use the signal pin as it is coming from arduino to the ESC. no need to level shift.