Arduino Rotary Encoder Pulses?
Add Serial.begin(115200); in setup() and use Serial.println() or Serial.print() to print to Serial.

In Arduino IDE open Serial Monitor and set baud rate to 115200.

EDIT: The question turned out to be about Serial Plotter. Maximilian Gerhardt answered in a comment :


  If you want multiple data streams (graphs) you need to seperate them
  by a comma: Serial.println( String(digitalRead(outputA)) + "," +
  String(digitalRead(outputB)));