Free virtual Uno simulation environment

Hi there, first of all; great program. Thumbs up!

I'm totally new at this and just practicing, so naturally i stumbled on something:

when i try to start an serial port with " Serial.begin(9600) " the program doesn't run.
When you write your program you'll see a black little screen with " BUILD-IN'S ",
if i look there there is an " //Serial: " that turns green (in the code)
but no " Serial. " , even if i type it in it stays black.

Does someone else have this problem, or see my misstep?

Ruud