In order to be able to interact with a MC, you must put it on your stage and give an instance name to it.
As you don't want your MC being visible from the start, you can let the first frame of your help MC empty (just with a stop() in the frame script).
In the second frame, you can place a label (i.e. "begin") and put the content of the new window.
Let's name the instance of your help MC: myHelpMc. The script on your button should be:
on release() {
_root.myHelpMc.gotoAndStop("begin");
}
If you want to close your help window, you should have another label on your help MC to make it invisible (i.e.: "end"). This frame have to be the same as first frame (just with the stop() action on it and nothing more)
If you have a button to close your help window, you can place the following script on it:
on release() {
_root.myHelpMc.gotoAndStop("end");
}
Thus, making it invisible again.
There is another way to get it, if you want to load your help window just at the time you push your button. In this case, you have to have a container MC on wich you load your new movie (the one that contains your help MC). When you want it to close, you have to unload the movie (commands loadMovie and unloadMovie)
I hope this is of any help