"Dimmer" noob question

Here's what I get:

Available serial ports:
Stable Library

Native lib Version = RXTX-2.1-7
Java lib Version = RXTX-2.1-7
[0] "COM1"
[1] "COM9"

And nothing happens...
What is going on here? Why is it that with the Nano it simply works, and with the Mega it's not?