I have the arbotix robocontroller and here is a picture of the led that I putted on the digital port:
and i want to turn on this led what sould i write at arduino to do this?
Is this an Arduino clone ?
First have a look at the sticky http://arduino.cc/forum/index.php/topic,97455.0.html
and some notes about LEDs
Then look at the example for "blink" and work from there through the examples.