how can i print out to console some variabels?
Serial.println(variable)
You will also need Serial.begin(9600) in your setup(), and a tool to read what’s written (the Arduino IDE has a serial console tool).
Does it have to be 9600 baud? I tried 115200 bps once, and very bad things happened.
Same here, tried something else, bad things happened. I stick to 9600 since. 
Thx it works just fine.
Finally figured out the flags of the keys 