How do I start a function with serial input?
Okay, as Majenko and Nick Gammon have suggested. The \n had not arrived in the serial buffer. That way the if clause was not fulfilled and nothing was printed. This code has worked for me now:

if (Serial.available() &gt; 0) {
 if (Serial.read() == 'A'){
  char inte1 = Serial.read();
  int inte2 = Serial.parseInt();
  int inte3 = Serial.parseInt();
  int inte4 = Serial.parseInt();
  int inte5 = Serial.parseInt();
  Serial.print(inte1);
  Serial.print(inte2);
  Serial.print(inte3);
  Serial.print(inte4);
  Serial.println(inte5);
 }
}


Although i read quite a bit now, serial input is still a mystery to me.