How do you play a movie clip?

is it:

_root.Quickmask.gotoAndPlay ("Playmark");?
_root[Quickmask].gotoAndPlay ("Playmark");?
_root["Quickmask"].gotoAndPlay ("Playmark");?
Quickmask.gotoAndPlay ("Playmark);?

The situation is:

A trigger/button on the main scene that calls a movie clip to be played. I keep on trying but I really can't make it work. Can someone help me plssss... or could someone send me .fla as my reference on how to play such movie .