Q 'bout MovieClip.prototype and functions

I had a look at the tutorial about the photo gallery and can’t quite work out the coding…

  1. What does the MovieClip in the coding represent? All the movie clips on the stage?

  2. out of the 5 functions in the code, 2 of them have “()” at the end and the other 3 don’t. Why is that? When I modified any of them my adding or removing brackets, the file doesn’t work anymore. What’s the difference between functions having “()” and not when called?

  3. What does the “trace(l/t)” do in the code? it doesn’t seem to display anything on the screen when testing the file…

thx in advance for your great help.