Looks like a typro/error in the reference, missing () after loop.
Here is the code that does not compile:
void setup(){
Serial.begin(9600);
}void loop(){
int i = 2;
int j = 3;
int k;k = myMultiplyFunction(i, j); // k now contains 6
Serial.println(k);
delay(500);
}int myMultiplyFunction(int x, int y){
int result;
result = x * y;
return result;
}