but i dont know if it counts in seconds
It will only count in seconds if you write the code to make it count in seconds. That code is very inefficient and there is a 1 second delay between each count. BUT the time taken to execute the code will make it count slightly slower.
Look at the blink without delay for how to use the timer function to synchronize your counter.
http://www.arduino.cc/en/Tutorial/BlinkWithoutDelay