L298 module - unusual power specs
That's a very poor datasheet. I think it's using equals signs where it means less-or-equal, so:


  High level: 2.3V = Vin = Vss 


Intends to say that Vin between 2.3 and Vss will be considered high, and 


  Low:-0.3V = Vin = 1.5V


Intends to say that Vin between -0.3 and 1.5V will be considered low. 

"Vss" in the high level definition is confusing, because in the rest of the datasheet, "VD" is used for the logic voltage and "VS" is used for the motor; you'd expect the upper limit to be the logic voltage.

The diagram at the end of the datasheet shows how it can be used with an Arduino. A 7.5V source is going into the Vin pin (instead of the barrel jack, which is unusual). There's a protection diode on the power input which incurs a ~1V voltage drop, so the Arduino Vin pin should be outputting 6.5V, which drives the board. The digital outs from the Arduino, when driven high, are at 5V, well above the 2.3V threshold given on the datasheet. 

I'd recommend powering the Arduino through the barrel jack with a 7.5V or 9V supply to drive the logic side of the board. (Powering through the USB port will put 5V or less on the Vin pin.) 

You'll want a more robust supply for the motor side, because the Arduino can't deliver very much current.