void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

  for (int i=0; i<10; i++){ //for(starting variable; condition for loop to continue; what we do to variable each time)
    Serial.println("Hello"); //if condition is met, code is excecuted
  }

  int i = 0; //counter must be made before while
  while (i<10){ //good for when you don't know how many times the loop must be repeated
    Serial.println("Hello World");
    i++; //counter must be inside while
  }
}

void loop() {
  // put your main code here, to run repeatedly:

}