Serial.println(): Where is the text printed?
The IDE on your computer has a menu item under the tools menu called "Serial Monitor." On my Mac, at least, it is indeed a black area under the source editor for the current sketch. 

It won't work unless you call the Serial.begin() function in your setup method before the first Serial.print()/println()/write() function call.

Something like this:

//Set up the serial port @ 9600 baud for display back to the computer
Serial.begin(9600);
delay(25);
Serial.println("Hello world!":);