How to interface a thermal printer to an Arduino
You might want to take a look at this library. The command set seems similar (for example Init is ESC + @). If anything, you can try to copy fragments of code for a simple printout.
Couple of things to consider:

Thermal printers need a stronger power supply. Get an external 9V power supply and connect it to the printer (not the Arduino!) - Seems like you did that.
Make sure GND on both the printer and board are connected.
Make sure the baudrate of the Arduino is compatible with the printer (e.g. Serial1.begin(19200);
Be patient. Hardware development is an art that fights back. Good luck!